Issues with sending attachments via RestSharp and Mailgun API

Other Questions Mailgun
1

I’m struggling to send attachments using RestSharp and the Mailgun API. The emails arrive, but the attachments are always about 302 bytes and corrupted. I’ve tried different methods:

  1. Using a file from the system with a hardcoded path
  2. Using binary data from a SQL Server database (varbinary(MAX) column)

Here’s what I’ve attempted:

// Method 1: Using database binary data
myRequest.AddFileBytes("file", dbRecord.BinaryContent.ToArray(), dbRecord.Name, "application/octet-stream");

// Method 2: Also using database binary data
myRequest.AddFile("file", dbRecord.BinaryContent.ToArray(), dbRecord.Name, "application/octet-stream");

// Method 3: Using a local file
string filePath = @"C:\Documents\Sample.docx";
myRequest.AddFile("file", filePath, "application/octet-stream");

The rest of the email sends fine. It’s just the attachments that are messed up. Any ideas what could be causing this?

2

Have you considered using the MailgunClient library instead of RestSharp? I switched to it recently and found it much easier to work with, especially for attachments. The syntax is more straightforward:

var message = new MessageBuilder()
    .AddAttachment(new FileInfo(filePath))
    .SetFrom("[email protected]")
    .SetSubject("Test Email")
    .SetText("This is a test email")
    .SetToRecipient("[email protected]")
    .GetMessage();

await client.SendMessageAsync(domain, message);

This handled all the MIME types and encoding for me automatically. If you’re set on using RestSharp, make sure you’re setting the correct Content-Type header for each attachment. Sometimes that can cause issues if it’s not matching the actual file type.

3

I’ve encountered similar issues with RestSharp and Mailgun before. From my experience, the problem often lies in how the file content is being read and transmitted. Here’s what worked for me:

Instead of using AddFile or AddFileBytes, try using AddParameter with the file content as a byte array. Something like this:

byte[] fileBytes = File.ReadAllBytes(filePath);
request.AddParameter("attachment", fileBytes, ParameterType.RequestBody);
request.AddHeader("Content-Type", "multipart/form-data");

This approach ensures the file content is properly encoded and sent as part of the multipart form data. Also, double-check that your Mailgun API key and domain are correctly set up.

If you’re still having issues, consider using Mailgun’s official C# SDK instead of RestSharp. It handles a lot of these edge cases out of the box and might save you some headaches in the long run.

4

hey, i had a similar problem. try using stream instead of byte array. something like this:

using (var stream = new FileStream(filePath, FileMode.Open))
{
request.AddFile(“attachment”, stream, Path.GetFileName(filePath));
}

this worked for me. also check ur content-type header, it shud match the file type ur sending.