diff --git a/src/Api/KeyManagement/Validators/SendRotationValidator.cs b/src/Api/KeyManagement/Validators/SendRotationValidator.cs
index 10a5d996b7..a781ab99ee 100644
--- a/src/Api/KeyManagement/Validators/SendRotationValidator.cs
+++ b/src/Api/KeyManagement/Validators/SendRotationValidator.cs
@@ -44,7 +44,7 @@ public class SendRotationValidator : IRotationValidator<IEnumerable<SendWithIdRe
                 throw new BadRequestException("All existing sends must be included in the rotation.");
             }
 
-            result.Add(send.ToSend(existing, _sendAuthorizationService));
+            result.Add(send.UpdateSend(existing, _sendAuthorizationService));
         }
 
         return result;
diff --git a/src/Api/Tools/Controllers/SendsController.cs b/src/Api/Tools/Controllers/SendsController.cs
index c4bf4595f3..71942469f1 100644
--- a/src/Api/Tools/Controllers/SendsController.cs
+++ b/src/Api/Tools/Controllers/SendsController.cs
@@ -92,7 +92,7 @@ public class SendsController : Controller
             throw new NotFoundException();
         }
 
-        var sendResponse = new SendAccessResponseModel(send, _globalSettings);
+        var sendResponse = new SendAccessResponseModel(send);
         if (send.UserId.HasValue && !send.HideEmail.GetValueOrDefault())
         {
             var creator = await _userService.GetUserByIdAsync(send.UserId.Value);
@@ -295,7 +295,7 @@ public class SendsController : Controller
             throw new NotFoundException();
         }
 
-        await _nonAnonymousSendCommand.SaveSendAsync(model.ToSend(send, _sendAuthorizationService));
+        await _nonAnonymousSendCommand.SaveSendAsync(model.UpdateSend(send, _sendAuthorizationService));
         return new SendResponseModel(send);
     }
 
@@ -309,7 +309,10 @@ public class SendsController : Controller
             throw new NotFoundException();
         }
 
+        // This endpoint exists because PUT preserves existing Password/Emails when not provided.
+        // This allows clients to update other fields without re-submitting sensitive auth data.
         send.Password = null;
+        send.AuthType = AuthType.None;
         await _nonAnonymousSendCommand.SaveSendAsync(send);
         return new SendResponseModel(send);
     }
diff --git a/src/Api/Tools/Models/Request/SendRequestModel.cs b/src/Api/Tools/Models/Request/SendRequestModel.cs
index 9f24329bbd..5a7ec6d146 100644
--- a/src/Api/Tools/Models/Request/SendRequestModel.cs
+++ b/src/Api/Tools/Models/Request/SendRequestModel.cs
@@ -24,6 +24,11 @@ public class SendRequestModel
     /// </summary>
     public SendType Type { get; set; }
 
+    /// <summary>
+    /// Specifies the authentication method required to access this Send.
+    /// </summary>
+    public AuthType? AuthType { get; set; }
+
     /// <summary>
     /// Estimated length of the file accompanying the send. <see langword="null"/> when
     /// <see cref="Type"/> is <see cref="SendType.Text"/>.
@@ -125,7 +130,7 @@ public class SendRequestModel
             Type = Type,
             UserId = (Guid?)userId
         };
-        ToSend(send, sendAuthorizationService);
+        send = UpdateSend(send, sendAuthorizationService);
         return send;
     }
 
@@ -155,8 +160,7 @@ public class SendRequestModel
     /// <param name="existingSend">The send to update</param>
     /// <param name="sendAuthorizationService">Hashes the send password.</param>
     /// <returns>The send object</returns>
-    // FIXME: rename to `UpdateSend`
-    public Send ToSend(Send existingSend, ISendAuthorizationService sendAuthorizationService)
+    public Send UpdateSend(Send existingSend, ISendAuthorizationService sendAuthorizationService)
     {
         existingSend = ToSendBase(existingSend, sendAuthorizationService);
         switch (existingSend.Type)
@@ -249,11 +253,29 @@ public class SendRequestModel
             var emails = Emails.Split(',', RemoveEmptyEntries | TrimEntries);
             existingSend.Emails = string.Join(", ", emails);
             existingSend.Password = null;
+            existingSend.AuthType = Core.Tools.Enums.AuthType.Email;
         }
         else if (!string.IsNullOrWhiteSpace(Password))
         {
             existingSend.Password = authorizationService.HashPassword(Password);
             existingSend.Emails = null;
+            existingSend.AuthType = Core.Tools.Enums.AuthType.Password;
+        }
+        else
+        {
+            // Neither Password nor Emails provided - preserve existing values and infer AuthType
+            if (!string.IsNullOrWhiteSpace(existingSend.Password))
+            {
+                existingSend.AuthType = Core.Tools.Enums.AuthType.Password;
+            }
+            else if (!string.IsNullOrWhiteSpace(existingSend.Emails))
+            {
+                existingSend.AuthType = Core.Tools.Enums.AuthType.Email;
+            }
+            else
+            {
+                existingSend.AuthType = Core.Tools.Enums.AuthType.None;
+            }
         }
 
         existingSend.Disabled = Disabled.GetValueOrDefault();
diff --git a/src/Api/Tools/Models/Response/SendAccessResponseModel.cs b/src/Api/Tools/Models/Response/SendAccessResponseModel.cs
index a466740d55..b722dd5fff 100644
--- a/src/Api/Tools/Models/Response/SendAccessResponseModel.cs
+++ b/src/Api/Tools/Models/Response/SendAccessResponseModel.cs
@@ -3,7 +3,6 @@
 
 using System.Text.Json;
 using Bit.Core.Models.Api;
-using Bit.Core.Settings;
 using Bit.Core.Tools.Entities;
 using Bit.Core.Tools.Enums;
 using Bit.Core.Tools.Models.Data;
@@ -20,17 +19,13 @@ public class SendAccessResponseModel : ResponseModel
     /// Instantiates a send access response model
     /// </summary>
     /// <param name="send">Content to transmit to the client.</param>
-    /// <param name="globalSettings">
-    /// Settings that control response generation.
-    /// </param>
     /// <exception cref="ArgumentNullException">
     /// Thrown when <paramref name="send"/> is <see langword="null" />
     /// </exception>
     /// <exception cref="ArgumentException">
     /// Thrown when <paramref name="send" /> has an invalid <see cref="Send.Type"/>.
     /// </exception>
-    // FIXME: remove `globalSettings` variable
-    public SendAccessResponseModel(Send send, GlobalSettings globalSettings)
+    public SendAccessResponseModel(Send send)
         : base("send-access")
     {
         if (send == null)
@@ -40,6 +35,7 @@ public class SendAccessResponseModel : ResponseModel
 
         Id = CoreHelpers.Base64UrlEncode(send.Id.ToByteArray());
         Type = send.Type;
+        AuthType = send.AuthType;
 
         SendData sendData;
         switch (send.Type)
@@ -72,6 +68,11 @@ public class SendAccessResponseModel : ResponseModel
     /// </summary>
     public SendType Type { get; set; }
 
+    /// <summary>
+    /// Specifies the authentication method required to access this Send.
+    /// </summary>
+    public AuthType? AuthType { get; set; }
+
     /// <summary>
     /// Label for the send. This is only visible to the owner of the send.
     /// </summary>
diff --git a/src/Api/Tools/Models/Response/SendResponseModel.cs b/src/Api/Tools/Models/Response/SendResponseModel.cs
index c8169252e5..569b8c13ce 100644
--- a/src/Api/Tools/Models/Response/SendResponseModel.cs
+++ b/src/Api/Tools/Models/Response/SendResponseModel.cs
@@ -37,6 +37,9 @@ public class SendResponseModel : ResponseModel
         Id = send.Id;
         AccessId = CoreHelpers.Base64UrlEncode(send.Id.ToByteArray());
         Type = send.Type;
+        AuthType = send.AuthType ?? (!string.IsNullOrWhiteSpace(send.Password)
+            ? AuthType = Core.Tools.Enums.AuthType.Password
+            : (!string.IsNullOrWhiteSpace(send.Emails)? Core.Tools.Enums.AuthType.Email : Core.Tools.Enums.AuthType.None));
         Key = send.Key;
         MaxAccessCount = send.MaxAccessCount;
         AccessCount = send.AccessCount;
@@ -84,6 +87,11 @@ public class SendResponseModel : ResponseModel
     /// </summary>
     public SendType Type { get; set; }
 
+    /// <summary>
+    /// Specifies the authentication method required to access this Send.
+    /// </summary>
+    public AuthType? AuthType { get; set; }
+
     /// <summary>
     /// Label for the send.
     /// </summary>
diff --git a/src/Core/Tools/Entities/Send.cs b/src/Core/Tools/Entities/Send.cs
index 34b68fd6c5..2daa2a6b30 100644
--- a/src/Core/Tools/Entities/Send.cs
+++ b/src/Core/Tools/Entities/Send.cs
@@ -37,6 +37,12 @@ public class Send : ITableObject<Guid>
     /// </summary>
     public SendType Type { get; set; }
 
+    /// <summary>
+    /// Specifies the authentication method required to access this Send.
+    /// </summary>
+    /// <seealso cref="Tools.Enums.AuthType"/>
+    public AuthType? AuthType { get; set; }
+
     /// <summary>
     /// Stores data containing or pointing to the transmitted secret. JSON.
     /// </summary>
diff --git a/src/Core/Tools/Enums/AuthType.cs b/src/Core/Tools/Enums/AuthType.cs
new file mode 100644
index 0000000000..814ebf69b8
--- /dev/null
+++ b/src/Core/Tools/Enums/AuthType.cs
@@ -0,0 +1,25 @@
+using System.Text.Json.Serialization;
+
+namespace Bit.Core.Tools.Enums;
+
+/// <summary>
+/// Specifies the authentication method required to access a Send.
+/// </summary>
+[JsonConverter(typeof(JsonStringEnumConverter))]
+public enum AuthType : byte
+{
+    /// <summary>
+    /// Email-based OTP authentication
+    /// </summary>
+    Email = 0,
+
+    /// <summary>
+    /// Password-based authentication
+    /// </summary>
+    Password = 1,
+
+    /// <summary>
+    /// No authentication required
+    /// </summary>
+    None = 2
+}
diff --git a/test/Api.Test/Tools/Controllers/SendsControllerTests.cs b/test/Api.Test/Tools/Controllers/SendsControllerTests.cs
index 885f7c1c7b..541e8a4903 100644
--- a/test/Api.Test/Tools/Controllers/SendsControllerTests.cs
+++ b/test/Api.Test/Tools/Controllers/SendsControllerTests.cs
@@ -3,6 +3,7 @@ using System.Text.Json;
 using AutoFixture.Xunit2;
 using Bit.Api.Models.Response;
 using Bit.Api.Tools.Controllers;
+using Bit.Api.Tools.Models;
 using Bit.Api.Tools.Models.Request;
 using Bit.Api.Tools.Models.Response;
 using Bit.Core.Entities;
@@ -173,4 +174,583 @@ public class SendsControllerTests : IDisposable
         Assert.Empty(result.Data);
         await _sendOwnerQuery.Received(1).GetOwned(Arg.Any<ClaimsPrincipal>());
     }
+
+    [Theory, AutoData]
+    public async Task Post_WithPassword_InfersAuthTypePassword(Guid userId)
+    {
+        _userService.GetProperUserId(Arg.Any<ClaimsPrincipal>()).Returns(userId);
+        var request = new SendRequestModel
+        {
+            Type = SendType.Text,
+            Key = "key",
+            Text = new SendTextModel { Text = "text" },
+            Password = "password",
+            DeletionDate = DateTime.UtcNow.AddDays(7)
+        };
+
+        var result = await _sut.Post(request);
+
+        Assert.NotNull(result);
+        Assert.Equal(AuthType.Password, result.AuthType);
+        await _nonAnonymousSendCommand.Received(1).SaveSendAsync(Arg.Is<Send>(s =>
+            s.AuthType == AuthType.Password &&
+            s.Password != null &&
+            s.Emails == null &&
+            s.UserId == userId &&
+            s.Type == SendType.Text));
+        _userService.Received(1).GetProperUserId(Arg.Any<ClaimsPrincipal>());
+    }
+
+    [Theory, AutoData]
+    public async Task Post_WithEmails_InfersAuthTypeEmail(Guid userId)
+    {
+        _userService.GetProperUserId(Arg.Any<ClaimsPrincipal>()).Returns(userId);
+        var request = new SendRequestModel
+        {
+            Type = SendType.Text,
+            Key = "key",
+            Text = new SendTextModel { Text = "text" },
+            Emails = "test@example.com",
+            DeletionDate = DateTime.UtcNow.AddDays(7)
+        };
+
+        var result = await _sut.Post(request);
+
+        Assert.NotNull(result);
+        Assert.Equal(AuthType.Email, result.AuthType);
+        await _nonAnonymousSendCommand.Received(1).SaveSendAsync(Arg.Is<Send>(s =>
+            s.AuthType == AuthType.Email &&
+            s.Emails != null &&
+            s.Password == null &&
+            s.UserId == userId &&
+            s.Type == SendType.Text));
+        _userService.Received(1).GetProperUserId(Arg.Any<ClaimsPrincipal>());
+    }
+
+    [Theory, AutoData]
+    public async Task Post_WithoutPasswordOrEmails_InfersAuthTypeNone(Guid userId)
+    {
+        _userService.GetProperUserId(Arg.Any<ClaimsPrincipal>()).Returns(userId);
+        var request = new SendRequestModel
+        {
+            Type = SendType.Text,
+            Key = "key",
+            Text = new SendTextModel { Text = "text" },
+            DeletionDate = DateTime.UtcNow.AddDays(7)
+        };
+
+        var result = await _sut.Post(request);
+
+        Assert.NotNull(result);
+        Assert.Equal(AuthType.None, result.AuthType);
+        await _nonAnonymousSendCommand.Received(1).SaveSendAsync(Arg.Is<Send>(s =>
+            s.AuthType == AuthType.None &&
+            s.Password == null &&
+            s.Emails == null &&
+            s.UserId == userId &&
+            s.Type == SendType.Text));
+        _userService.Received(1).GetProperUserId(Arg.Any<ClaimsPrincipal>());
+    }
+
+    [Theory]
+    [InlineData(AuthType.Password)]
+    [InlineData(AuthType.Email)]
+    [InlineData(AuthType.None)]
+    public async Task Access_ReturnsCorrectAuthType(AuthType authType)
+    {
+        var sendId = Guid.NewGuid();
+        var accessId = CoreHelpers.Base64UrlEncode(sendId.ToByteArray());
+        var send = new Send
+        {
+            Id = sendId,
+            Type = SendType.Text,
+            Data = JsonSerializer.Serialize(new Dictionary<string, string>()),
+            AuthType = authType
+        };
+
+        _sendRepository.GetByIdAsync(sendId).Returns(send);
+        _sendAuthorizationService.AccessAsync(send, "pwd123").Returns(SendAccessResult.Granted);
+
+        var request = new SendAccessRequestModel();
+        var actionResult = await _sut.Access(accessId, request);
+        var response = (actionResult as ObjectResult)?.Value as SendAccessResponseModel;
+
+        Assert.NotNull(response);
+        Assert.Equal(authType, response.AuthType);
+    }
+
+    [Theory]
+    [InlineData(AuthType.Password)]
+    [InlineData(AuthType.Email)]
+    [InlineData(AuthType.None)]
+    public async Task Get_ReturnsCorrectAuthType(AuthType authType)
+    {
+        var sendId = Guid.NewGuid();
+        var send = new Send
+        {
+            Id = sendId,
+            Type = SendType.Text,
+            Data = JsonSerializer.Serialize(new SendTextData("a", "b", "c", false)),
+            AuthType = authType
+        };
+
+        _sendOwnerQuery.Get(sendId, Arg.Any<ClaimsPrincipal>()).Returns(send);
+
+        var result = await _sut.Get(sendId.ToString());
+
+        Assert.NotNull(result);
+        Assert.Equal(authType, result.AuthType);
+    }
+
+    [Theory, AutoData]
+    public async Task Put_WithValidSend_UpdatesSuccessfully(Guid userId, Guid sendId)
+    {
+        _userService.GetProperUserId(Arg.Any<ClaimsPrincipal>()).Returns(userId);
+        var existingSend = new Send
+        {
+            Id = sendId,
+            UserId = userId,
+            Type = SendType.Text,
+            Data = JsonSerializer.Serialize(new SendTextData("Old", "Old notes", "Old text", false)),
+            AuthType = AuthType.None
+        };
+        _sendRepository.GetByIdAsync(sendId).Returns(existingSend);
+
+        var request = new SendRequestModel
+        {
+            Type = SendType.Text,
+            Key = "updated-key",
+            Text = new SendTextModel { Text = "updated text" },
+            Password = "new-password",
+            DeletionDate = DateTime.UtcNow.AddDays(7)
+        };
+
+        var result = await _sut.Put(sendId.ToString(), request);
+
+        Assert.NotNull(result);
+        Assert.Equal(sendId, result.Id);
+        await _nonAnonymousSendCommand.Received(1).SaveSendAsync(Arg.Is<Send>(s => s.Id == sendId));
+    }
+
+    [Theory, AutoData]
+    public async Task Put_WithNonExistentSend_ThrowsNotFoundException(Guid userId, Guid sendId)
+    {
+        _userService.GetProperUserId(Arg.Any<ClaimsPrincipal>()).Returns(userId);
+        _sendRepository.GetByIdAsync(sendId).Returns((Send)null);
+
+        var request = new SendRequestModel
+        {
+            Type = SendType.Text,
+            Key = "key",
+            Text = new SendTextModel { Text = "text" },
+            DeletionDate = DateTime.UtcNow.AddDays(7)
+        };
+
+        await Assert.ThrowsAsync<NotFoundException>(() => _sut.Put(sendId.ToString(), request));
+    }
+
+    [Theory, AutoData]
+    public async Task Put_WithWrongUser_ThrowsNotFoundException(Guid userId, Guid otherUserId, Guid sendId)
+    {
+        _userService.GetProperUserId(Arg.Any<ClaimsPrincipal>()).Returns(userId);
+        var existingSend = new Send
+        {
+            Id = sendId,
+            UserId = otherUserId,
+            Type = SendType.Text,
+            Data = JsonSerializer.Serialize(new SendTextData("Old", "Old notes", "Old text", false))
+        };
+        _sendRepository.GetByIdAsync(sendId).Returns(existingSend);
+
+        var request = new SendRequestModel
+        {
+            Type = SendType.Text,
+            Key = "key",
+            Text = new SendTextModel { Text = "text" },
+            DeletionDate = DateTime.UtcNow.AddDays(7)
+        };
+
+        await Assert.ThrowsAsync<NotFoundException>(() => _sut.Put(sendId.ToString(), request));
+    }
+
+    [Theory, AutoData]
+    public async Task PutRemovePassword_WithValidSend_RemovesPasswordAndSetsAuthTypeNone(Guid userId, Guid sendId)
+    {
+        _userService.GetProperUserId(Arg.Any<ClaimsPrincipal>()).Returns(userId);
+        var existingSend = new Send
+        {
+            Id = sendId,
+            UserId = userId,
+            Type = SendType.Text,
+            Data = JsonSerializer.Serialize(new SendTextData("Test", "Notes", "Text", false)),
+            Password = "hashed-password",
+            AuthType = AuthType.Password
+        };
+        _sendRepository.GetByIdAsync(sendId).Returns(existingSend);
+
+        var result = await _sut.PutRemovePassword(sendId.ToString());
+
+        Assert.NotNull(result);
+        Assert.Equal(sendId, result.Id);
+        Assert.Equal(AuthType.None, result.AuthType);
+        await _nonAnonymousSendCommand.Received(1).SaveSendAsync(Arg.Is<Send>(s =>
+            s.Id == sendId &&
+            s.Password == null &&
+            s.AuthType == AuthType.None));
+    }
+
+    [Theory, AutoData]
+    public async Task PutRemovePassword_WithNonExistentSend_ThrowsNotFoundException(Guid userId, Guid sendId)
+    {
+        _userService.GetProperUserId(Arg.Any<ClaimsPrincipal>()).Returns(userId);
+        _sendRepository.GetByIdAsync(sendId).Returns((Send)null);
+
+        await Assert.ThrowsAsync<NotFoundException>(() => _sut.PutRemovePassword(sendId.ToString()));
+    }
+
+    [Theory, AutoData]
+    public async Task PutRemovePassword_WithWrongUser_ThrowsNotFoundException(Guid userId, Guid otherUserId, Guid sendId)
+    {
+        _userService.GetProperUserId(Arg.Any<ClaimsPrincipal>()).Returns(userId);
+        var existingSend = new Send
+        {
+            Id = sendId,
+            UserId = otherUserId,
+            Type = SendType.Text,
+            Data = JsonSerializer.Serialize(new SendTextData("Test", "Notes", "Text", false)),
+            Password = "hashed-password"
+        };
+        _sendRepository.GetByIdAsync(sendId).Returns(existingSend);
+
+        await Assert.ThrowsAsync<NotFoundException>(() => _sut.PutRemovePassword(sendId.ToString()));
+    }
+
+    [Theory, AutoData]
+    public async Task Delete_WithValidSend_DeletesSuccessfully(Guid userId, Guid sendId)
+    {
+        _userService.GetProperUserId(Arg.Any<ClaimsPrincipal>()).Returns(userId);
+        var existingSend = new Send
+        {
+            Id = sendId,
+            UserId = userId,
+            Type = SendType.Text,
+            Data = JsonSerializer.Serialize(new SendTextData("Test", "Notes", "Text", false))
+        };
+        _sendRepository.GetByIdAsync(sendId).Returns(existingSend);
+
+        await _sut.Delete(sendId.ToString());
+
+        await _nonAnonymousSendCommand.Received(1).DeleteSendAsync(Arg.Is<Send>(s => s.Id == sendId));
+    }
+
+    [Theory, AutoData]
+    public async Task Delete_WithNonExistentSend_ThrowsNotFoundException(Guid userId, Guid sendId)
+    {
+        _userService.GetProperUserId(Arg.Any<ClaimsPrincipal>()).Returns(userId);
+        _sendRepository.GetByIdAsync(sendId).Returns((Send)null);
+
+        await Assert.ThrowsAsync<NotFoundException>(() => _sut.Delete(sendId.ToString()));
+    }
+
+    [Theory, AutoData]
+    public async Task Delete_WithWrongUser_ThrowsNotFoundException(Guid userId, Guid otherUserId, Guid sendId)
+    {
+        _userService.GetProperUserId(Arg.Any<ClaimsPrincipal>()).Returns(userId);
+        var existingSend = new Send
+        {
+            Id = sendId,
+            UserId = otherUserId,
+            Type = SendType.Text,
+            Data = JsonSerializer.Serialize(new SendTextData("Test", "Notes", "Text", false))
+        };
+        _sendRepository.GetByIdAsync(sendId).Returns(existingSend);
+
+        await Assert.ThrowsAsync<NotFoundException>(() => _sut.Delete(sendId.ToString()));
+    }
+
+    [Theory, AutoData]
+    public async Task PostFile_WithPassword_InfersAuthTypePassword(Guid userId)
+    {
+        _userService.GetProperUserId(Arg.Any<ClaimsPrincipal>()).Returns(userId);
+        _nonAnonymousSendCommand.SaveFileSendAsync(Arg.Any<Send>(), Arg.Any<SendFileData>(), Arg.Any<long>())
+            .Returns("https://example.com/upload")
+            .AndDoes(callInfo =>
+            {
+                var send = callInfo.ArgAt<Send>(0);
+                var data = callInfo.ArgAt<SendFileData>(1);
+                send.Data = JsonSerializer.Serialize(data);
+            });
+
+        var request = new SendRequestModel
+        {
+            Type = SendType.File,
+            Key = "key",
+            File = new SendFileModel { FileName = "test.txt" },
+            FileLength = 1024L,
+            Password = "password",
+            DeletionDate = DateTime.UtcNow.AddDays(7)
+        };
+
+        var result = await _sut.PostFile(request);
+
+        Assert.NotNull(result);
+        Assert.NotNull(result.SendResponse);
+        Assert.Equal(AuthType.Password, result.SendResponse.AuthType);
+        await _nonAnonymousSendCommand.Received(1).SaveFileSendAsync(
+            Arg.Is<Send>(s =>
+                s.AuthType == AuthType.Password &&
+                s.Password != null &&
+                s.Emails == null &&
+                s.UserId == userId),
+            Arg.Any<SendFileData>(),
+            1024L);
+    }
+
+    [Theory, AutoData]
+    public async Task PostFile_WithEmails_InfersAuthTypeEmail(Guid userId)
+    {
+        _userService.GetProperUserId(Arg.Any<ClaimsPrincipal>()).Returns(userId);
+        _nonAnonymousSendCommand.SaveFileSendAsync(Arg.Any<Send>(), Arg.Any<SendFileData>(), Arg.Any<long>())
+            .Returns("https://example.com/upload")
+            .AndDoes(callInfo =>
+            {
+                var send = callInfo.ArgAt<Send>(0);
+                var data = callInfo.ArgAt<SendFileData>(1);
+                send.Data = JsonSerializer.Serialize(data);
+            });
+
+        var request = new SendRequestModel
+        {
+            Type = SendType.File,
+            Key = "key",
+            File = new SendFileModel { FileName = "test.txt" },
+            FileLength = 1024L,
+            Emails = "test@example.com",
+            DeletionDate = DateTime.UtcNow.AddDays(7)
+        };
+
+        var result = await _sut.PostFile(request);
+
+        Assert.NotNull(result);
+        Assert.NotNull(result.SendResponse);
+        Assert.Equal(AuthType.Email, result.SendResponse.AuthType);
+        await _nonAnonymousSendCommand.Received(1).SaveFileSendAsync(
+            Arg.Is<Send>(s =>
+                s.AuthType == AuthType.Email &&
+                s.Emails != null &&
+                s.Password == null &&
+                s.UserId == userId),
+            Arg.Any<SendFileData>(),
+            1024L);
+    }
+
+    [Theory, AutoData]
+    public async Task PostFile_WithoutPasswordOrEmails_InfersAuthTypeNone(Guid userId)
+    {
+        _userService.GetProperUserId(Arg.Any<ClaimsPrincipal>()).Returns(userId);
+        _nonAnonymousSendCommand.SaveFileSendAsync(Arg.Any<Send>(), Arg.Any<SendFileData>(), Arg.Any<long>())
+            .Returns("https://example.com/upload")
+            .AndDoes(callInfo =>
+            {
+                var send = callInfo.ArgAt<Send>(0);
+                var data = callInfo.ArgAt<SendFileData>(1);
+                send.Data = JsonSerializer.Serialize(data);
+            });
+
+        var request = new SendRequestModel
+        {
+            Type = SendType.File,
+            Key = "key",
+            File = new SendFileModel { FileName = "test.txt" },
+            FileLength = 1024L,
+            DeletionDate = DateTime.UtcNow.AddDays(7)
+        };
+
+        var result = await _sut.PostFile(request);
+
+        Assert.NotNull(result);
+        Assert.NotNull(result.SendResponse);
+        Assert.Equal(AuthType.None, result.SendResponse.AuthType);
+        await _nonAnonymousSendCommand.Received(1).SaveFileSendAsync(
+            Arg.Is<Send>(s =>
+                s.AuthType == AuthType.None &&
+                s.Password == null &&
+                s.Emails == null &&
+                s.UserId == userId),
+            Arg.Any<SendFileData>(),
+            1024L);
+    }
+
+    [Theory, AutoData]
+    public async Task Put_ChangingFromPasswordToEmails_UpdatesAuthTypeToEmail(Guid userId, Guid sendId)
+    {
+        _userService.GetProperUserId(Arg.Any<ClaimsPrincipal>()).Returns(userId);
+        var existingSend = new Send
+        {
+            Id = sendId,
+            UserId = userId,
+            Type = SendType.Text,
+            Data = JsonSerializer.Serialize(new SendTextData("Old", "Old notes", "Old text", false)),
+            Password = "hashed-password",
+            AuthType = AuthType.Password
+        };
+        _sendRepository.GetByIdAsync(sendId).Returns(existingSend);
+
+        var request = new SendRequestModel
+        {
+            Type = SendType.Text,
+            Key = "updated-key",
+            Text = new SendTextModel { Text = "updated text" },
+            Emails = "new@example.com",
+            DeletionDate = DateTime.UtcNow.AddDays(7)
+        };
+
+        var result = await _sut.Put(sendId.ToString(), request);
+
+        Assert.NotNull(result);
+        Assert.Equal(sendId, result.Id);
+        await _nonAnonymousSendCommand.Received(1).SaveSendAsync(Arg.Is<Send>(s =>
+            s.Id == sendId &&
+            s.AuthType == AuthType.Email &&
+            s.Emails != null &&
+            s.Password == null));
+    }
+
+    [Theory, AutoData]
+    public async Task Put_ChangingFromEmailToPassword_UpdatesAuthTypeToPassword(Guid userId, Guid sendId)
+    {
+        _userService.GetProperUserId(Arg.Any<ClaimsPrincipal>()).Returns(userId);
+        var existingSend = new Send
+        {
+            Id = sendId,
+            UserId = userId,
+            Type = SendType.Text,
+            Data = JsonSerializer.Serialize(new SendTextData("Old", "Old notes", "Old text", false)),
+            Emails = "old@example.com",
+            AuthType = AuthType.Email
+        };
+        _sendRepository.GetByIdAsync(sendId).Returns(existingSend);
+
+        var request = new SendRequestModel
+        {
+            Type = SendType.Text,
+            Key = "updated-key",
+            Text = new SendTextModel { Text = "updated text" },
+            Password = "new-password",
+            DeletionDate = DateTime.UtcNow.AddDays(7)
+        };
+
+        var result = await _sut.Put(sendId.ToString(), request);
+
+        Assert.NotNull(result);
+        Assert.Equal(sendId, result.Id);
+        await _nonAnonymousSendCommand.Received(1).SaveSendAsync(Arg.Is<Send>(s =>
+            s.Id == sendId &&
+            s.AuthType == AuthType.Password &&
+            s.Password != null &&
+            s.Emails == null));
+    }
+
+    [Theory, AutoData]
+    public async Task Put_WithoutPasswordOrEmails_PreservesExistingPassword(Guid userId, Guid sendId)
+    {
+        _userService.GetProperUserId(Arg.Any<ClaimsPrincipal>()).Returns(userId);
+        var existingSend = new Send
+        {
+            Id = sendId,
+            UserId = userId,
+            Type = SendType.Text,
+            Data = JsonSerializer.Serialize(new SendTextData("Old", "Old notes", "Old text", false)),
+            Password = "hashed-password",
+            AuthType = AuthType.Password
+        };
+        _sendRepository.GetByIdAsync(sendId).Returns(existingSend);
+
+        var request = new SendRequestModel
+        {
+            Type = SendType.Text,
+            Key = "updated-key",
+            Text = new SendTextModel { Text = "updated text" },
+            DeletionDate = DateTime.UtcNow.AddDays(7)
+        };
+
+        var result = await _sut.Put(sendId.ToString(), request);
+
+        Assert.NotNull(result);
+        Assert.Equal(sendId, result.Id);
+        await _nonAnonymousSendCommand.Received(1).SaveSendAsync(Arg.Is<Send>(s =>
+            s.Id == sendId &&
+            s.AuthType == AuthType.Password &&
+            s.Password == "hashed-password" &&
+            s.Emails == null));
+    }
+
+    [Theory, AutoData]
+    public async Task Put_WithoutPasswordOrEmails_PreservesExistingEmails(Guid userId, Guid sendId)
+    {
+        _userService.GetProperUserId(Arg.Any<ClaimsPrincipal>()).Returns(userId);
+        var existingSend = new Send
+        {
+            Id = sendId,
+            UserId = userId,
+            Type = SendType.Text,
+            Data = JsonSerializer.Serialize(new SendTextData("Old", "Old notes", "Old text", false)),
+            Emails = "test@example.com",
+            AuthType = AuthType.Email
+        };
+        _sendRepository.GetByIdAsync(sendId).Returns(existingSend);
+
+        var request = new SendRequestModel
+        {
+            Type = SendType.Text,
+            Key = "updated-key",
+            Text = new SendTextModel { Text = "updated text" },
+            DeletionDate = DateTime.UtcNow.AddDays(7)
+        };
+
+        var result = await _sut.Put(sendId.ToString(), request);
+
+        Assert.NotNull(result);
+        Assert.Equal(sendId, result.Id);
+        await _nonAnonymousSendCommand.Received(1).SaveSendAsync(Arg.Is<Send>(s =>
+            s.Id == sendId &&
+            s.AuthType == AuthType.Email &&
+            s.Emails == "test@example.com" &&
+            s.Password == null));
+    }
+
+    [Theory, AutoData]
+    public async Task Put_WithoutPasswordOrEmails_PreservesNoneAuthType(Guid userId, Guid sendId)
+    {
+        _userService.GetProperUserId(Arg.Any<ClaimsPrincipal>()).Returns(userId);
+        var existingSend = new Send
+        {
+            Id = sendId,
+            UserId = userId,
+            Type = SendType.Text,
+            Data = JsonSerializer.Serialize(new SendTextData("Old", "Old notes", "Old text", false)),
+            Password = null,
+            Emails = null,
+            AuthType = AuthType.None
+        };
+        _sendRepository.GetByIdAsync(sendId).Returns(existingSend);
+
+        var request = new SendRequestModel
+        {
+            Type = SendType.Text,
+            Key = "updated-key",
+            Text = new SendTextModel { Text = "updated text" },
+            DeletionDate = DateTime.UtcNow.AddDays(7)
+        };
+
+        var result = await _sut.Put(sendId.ToString(), request);
+
+        Assert.NotNull(result);
+        Assert.Equal(sendId, result.Id);
+        await _nonAnonymousSendCommand.Received(1).SaveSendAsync(Arg.Is<Send>(s =>
+            s.Id == sendId &&
+            s.AuthType == AuthType.None &&
+            s.Password == null &&
+            s.Emails == null));
+    }
 }