I have a raspberry pi running postfix. I Realised unless I open port 25 I absolutely cannot receive emails (I have 587 open and can send but not receive them). However I heard there are scaries online which someone could potentially send emails from your server without consent. I believe as well my ISP doesn’t block port 25. Is there anything I should do right now before opening port 25, or should everything be safe enough?
IMHO a RasPi is just not reliable enough. Your internet connection is just not reliable enough. You are going to lose some of your incoming mail and NOT notice it, unless you have somebody who hosts a secondary MX for your domain.
Chances are also that it’s not powerful enough when some of these automated attacks come knocking.
If you know how to set it up, RPI can be reliable enough
Even, IMAP is TCP already, any coming mail should be cached by the router until delivered, and your router usually doesn’t loose connection as often as the connected devices