i got the answer. It is the "to" and "bcc" field setup problem.
I used to like set bcc field to send mail, but GAE did't allow me to only set bcc. Then i set the "to" and "bcc" field at the same time, and for the gmail recipients, the gmail server will filter the same mail for duplicate mails. That is why gmail recipients only get one mail, but the other mail servers will get twice. -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To view this discussion on the web visit https://groups.google.com/d/msg/google-appengine/-/hulIduGlYeUJ. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
