I have a situation that I don’t think can be all that unusual - I have multiple email accounts in different domains on the same MIAB instance. I can’t make this work reliably because of a stupid feature of iOS mail.
iOS mail lets you define multiple email accounts, however, the outbound SMTP accounts are treated like a pool - it will try each in turn until it finds a login that works. This causes a problem because it thinks that “works” means “auth is successful”. Say I have user@d1.com and user@d2.com defined, both have an outbound SMTP server defined that happens to be the same MIAB server; in the pool, one of these will be tried first. So if I send from the user@d1.com account, it tries the first definition (logging in as user@d1.com), successfully logs into the mail server and sends successfully. If I then send from user@d2.com, it tries the same list - logs into the server successfully as user@d1.com, but fails to send because user@d2.com can’t send as user@d1.com, but because the login was successful, it does not try the other accounts in the SMTP server list (especially since the server for d2.com has the same name, so it assumes that it will fail too).
The workaround for this is to go into the settings for the user@d1.com account and disable its SMTP server. This causes it to try the next SMTP server in the list (as user@d2.com), which is then successful. But of course this then means that sending as user@d1.com no longer works. This is bad enough with 2 accounts, but I have about 12.
Clearly this is a bit of stupid design in the iOS mail app - the macOS desktop app doesn’t share the problem as it lets you specify an explicit SMTP server for each account.
On my old mail server this wasn’t a problem because it would allow you to send as any supported domain if you had a working login for any account - so user@d2.com could send using a user@d1.com login. I’m in the fortunate situation of being able to trust all my users, so is there Is there some way of relaxing the sending policy in MIAB in the same way?
Or should I try to “trick” iOS mail into thinking that each account has a different mail server by creating different names pointing at the same server - or will that create issues with reverse DNS no longer matching?
