AWS SDK .NET - SES V2 Sending Wrong Attachment File

The issue you're experiencing with sending the wrong attachment file via AWS SES V2 using the .NET SDK could have several potential causes. Let's explore some possibilities:

1. Memory Stream Handling:

   • Ensure that you're properly handling the MemoryStream. The stream should be positioned at the beginning (Position = 0) before reading or converting it to base64.
   • Verify that the stream is not being closed or disposed of prematurely.

2. Base64 Encoding:

   • Double-check your base64 encoding process. Incorrect encoding can lead to corrupted attachments.
   • Make sure you're using a reliable method to convert the MemoryStream to base64, such as Convert.ToBase64String().

3. Content-Transfer-Encoding:

   • Ensure that you've set the correct Content-Transfer-Encoding for your attachment. For binary files like PDFs, it should typically be set to "base64".

4. MIME Type:

   • Verify that you're using the correct MIME type for your PDF attachment (application/pdf).

5. Attachment Object Structure:

   • Make sure your attachment object includes all necessary fields: FileName, ContentType, ContentDisposition, ContentDescription, RawContent, and ContentTransferEncoding.

6. File Reading:

   • If you're reading the PDF from a file before creating the MemoryStream, ensure that you're reading it in binary mode.

7. SDK Version:

   • Ensure you're using the latest version of the AWS SDK for .NET, as older versions might have bugs that could cause this issue.

8. File Size:

   • Check if the issue occurs with smaller PDF files. If smaller files work correctly, there might be an issue with handling larger attachments.

9. Email Client Compatibility:

   • Test the email with different email clients to rule out any client-specific rendering issues.

To troubleshoot further:

• Log the size of the MemoryStream before and after base64 encoding.
• Try sending the same PDF using the AWS CLI to determine if it's an SDK-specific issue.
• Verify the raw content of the email, including headers and attachment encoding, to ensure everything is formatted correctly.

If the issue persists after checking these potential causes, you may need to review your code for any logical errors in handling the PDF file or constructing the email message.
Sources
Working with email attachments in SES - Amazon Simple Email Service
How can I use SES V2 API send email with attachment? | AWS re:Post