Google App Engine Emails Going to SPAM folder

When I send emails through google app engine using the mail's send_mail function, they often get placed in the receiver's SPAM folder. Although this problem does not happen for GMail accounts, it does for Yahoo Mail accounts (and开发者_高级运维 presumably several others)

Is there a way to get the emails GAE sends around the SPAM filter?

This is going to depend a great deal on what about the messages you're sending gets them marked as spam. Google's documentation suggests that it's the app engine that actually does the SMTP, so there might be some other google app engine app that someone's marked as spam and your sending IP (which happens to be the same) is getting tarred with the same brush, or it might be something about the content of your messages. Many big mail providers give you some way to determine how 'spammy' they'll think a particular message will be; perhaps you could get information that way?

Another option is the standard 'be careful to add [some address] to your safe senders list if you want to get email from us!' warning in your app.

See this reasoning, provided by Gmail on how it filters incoming email based on the header information. The key thing to note here is that all emails sent via GAE's SMTP infrastructure are sent via email IDs of the format xyz.apphosting.bounces.google.com, which by Gmail's definition itself brings the emails under the category of falsely / apparently bounced email messages, hence they get categorized as spam. The same would hold true for other email service providers that follow similar logic for spam filtering.

GAE still needs to come up with a good solution to this problem. In the meanwhile, the suggestion I would give you is to use an external email service. Since GAE does not allow you to open arbitrary TCP sockets, you can use the URLFetch service to submit requests to external services that can open SMTP connections and send email on behalf of your email ID.

While this approach shifts your email sending costs to the external service, it consumes additional GAE resources, namely- UrlFetch service API calls and UrlFetch Data sent.

Update: Google App Engine plans to launch support for outbound sockets soon as part of their production feature roadmap, so making external SMTP connections directly would become a possibility.