Okay, but it's not really fixed my code. However, it makes me think there is some documentation or news regarding the limit. I found it here. So, I decided to ask Amazon Q to increase the attachment limit.
Of course, the issue still exists; it seems the PDF has been corrupted when sending the email. I've checked the size when downloading, it has the correct size. But the attached file size was doubled. So, I decided to ask Amazon Q to compress it.
Very unfortunate, I can't open the zip file! So, I think the bug occurs when sending the base64 data, which introduces a corrupted file.
I hope it will be fixed when I identify the SDK with Amazon Q later. But not now, sorry.
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Voila! I fixed it just by providing ContentTransferEncoding = "BASE64". The SDK always converts my file to base64, but the encoding was being set to SEVEN_BIT. Of course, it's not matched encoding!
