evan.yates I'm going to "spitball" here in lieu of a confirmed solution. I suspect multiple file attachments is something we may ultimately need to raise with the platform team as a feature request.
The first thing that jumps out at me is that it sounds like the downloaded files may be being stored in a format different from the original. In HTTP downloads (outside of Workato) you can specify a content-type in the request, and that defines the way the file is saved. Think text/html, image/jpeg, etc. So I'm wondering if this is an area to seek validation of the source and written file formats actually are.
Second, if there's only an option to attach one file, perhaps you could zip the files into a single archive and attach that? The problem with this is that Zip files are seen as an attack vector and often rejected by the receiving email system.
Another option might be to include the pre-signed URLs in the email body. This would allow the user to download the files directly, albeit I believe there is an expiration date on the URLs, which would prevent downloading if not done in a reasonable period of time. That creates more problems.
Regarding Mail for Workato, I suspect our email address is used because we manage "Email Authentication" (SPF, DKIM, DMARC) to ensure delivery. We don't support custom email address likely due to the complexity of configuring email auth.
This actually inspires my final idea. What about creating a custom action using Python and "rolling your own" email delivery agent? You could possibly relay email through your Microsoft org using SMTP Auth on a dedicated acoount, through an SMTP API if they offer one. Although this is fraught with some complexities, it might be possible.
Lastly, I think this is worth bringing up with your Customer Success Manager, they might have suggestions I have missed, and it also helps to circulate product feedback. I'm happy to ideate here as well.
