unable to send mail with zip attachment over google app engine

Question

I tried sending an e-mail with a pdf attachment over google app engine and it worked. I then used the same code with a zip file. The recipient didnt receive the mail. When I checked the logs in Google App Engine, no errors were reported either. What could be going wrong? Can someone please tell me if it is possible to send zip files over mail as attachments using Goog app engine? If yes, can you please tell me how to do it?

Answer 1

Here is a list of mime types that are allowed as attachments according to the docs. Zip files are not on the allowed list, while pdf files are.

Answer 2

I suspect (in the absence of further info) that your recipient's mail server/hosting will have possibly binned the mail with the .zip for being a potential virus. Many enterprises will have particular rules for accepting/rejecting mail based on attachments, and .zip files are a popular candidate for rejection.

If you can reliably send a .pdf, and reliably fail to send a .zip (of similar size) then this is the likely issue.

Answer 3

It is possible your Mail was filtered out on the recipient's end rather than by the App engine.

Try re-sending the mail to an address that has neither spam no virus protection, or a spam folder you can check.

Otherwise, make a size comparison (Is the zip file too large on either your, or the recipient's end?) and make sure you have a proper return address so you get informed about errors.

Answer 4

In addition to being filtered at the recipient side, Google's SMTP servers will reject sending certain attachments deemed as "dangerous", although I'm not sure if/how that would surface as an error in app engine. May want to try sending with an attachment you know would/should be rejected (some windows exe, for instance) as a comparison.

The contents of the zip file may also make a difference (many SMTP servers will look inside them), so try a zip file that only contains the pdf that worked as another data point.