We have a program that has the capability of sending and receiving email. Consider that many users are connecting through an ISP to the internet. The problem that we sometimes encounter is that we are sending an email directly through to our SMTP server and the ISP does not like that, for obvious reasons. I believe the process goes as follows:
1. user sends email to firstname.lastname@example.org using mailserver.ourdomain.com
2. traffic gets to ISP, ISP checks that the email is not using their SMTP server and sometimes drops this request
We do not want the user to bother with finding out their login info and ISP SMTP server address, that is not an option. So far, we only have work arounds to this and would like to know what options we have to do this. For instance, http traffic is never dropped so perhaps there is a way of carrying the email inside an http request. One more thing to note is that webmail per se is not an option, there are/will be too many users so an apache/imap/webmail solution is not an option.
Any suggestions are welcome.