Does a receiving mail server (the ultimate destination) see emails delivered directly to it vs. to an external relay which then forwards them to it?
- by Matt
Let's say my users have accounts on some mail server mail.example.com. I currently have my mx record set to mail.example.com and all is good. Now let's say I want to have mails initially delivered to an external service (e.g. Postini. Note that this is not a postini-specific question though).
In the normal situation where my mx is set directly to my mail server mail.example.com, sending MTAs will of course look up my MX and send to mail.example.com. In my new situation I'd have my mx set to mx.othermailservice.com and emails would be received there. OtherEmailService.com will then relay the emails (while keeping the return-path header the same) to mail.example.com. Do the emails that are received at mail.example.com after be relayed from the other service "look" any different than emails that go directly to it as would be the case where the mx was set to mail.example.com?