AWS-SES sending from one site, from is another site - will DMARC help or hurt

Question

Alright, to keep this simple:

I have a project that is using AWS's SES to send transactional emails. The project is hosted on one site (let's call it example-site.com), but for reasons, the From: is going to be from another site (example-site-two.com).

Now, I already have DKIM set up on both sites. I do NOT have DMARC set up on either site.

When I send test emails with attachments to a Gmail account, it works fine. The email arrives, the attachment is attached and readable. (It's a PDF for what that's worth.)

If I send the same email (and same attachment) to a yahoo.com or outlook.com email address, however, the email arrives, but the attachment is "blanked out". It's 0 bytes, but still has the correct file name.

Is this because I don't have DMARC set up? Or is this just because Yahoo and Outlook are being fussy? And will adding DMARC records to example-site.com and example-site-two.com mess things up? Like I said, this is technically being sent from one site, but I'm setting the From: field in the code to an email address from a different site.

Answer 1

This issue shouldn't be related to DMARC. It's likely that there's a problem with the emails you are sending. Gmail is generally more tolerant of malformed emails than Yahoo Mail and Outlook.

For instance, consider this question on Stack Overflow, where a missing blank line between the attachment header and the attachment contents was the culprit.