Let me start by saying, I don't use Mikrotik routers. My situation is as follows:
A company hired me to build them an on-premise Exchange server.(Not sure why, they have in-house IT). I set them up with a 3rd party email filtering service and I really want to use best practices and limit inbound connections on the smtp port to only the IPs provided by the email filter. I'm not familiar with these routers at all, and I can't seem to find any documentation specific to this need. They pay another company to monitor their firewall for them and that company outright refuses to create this rule for me. I managed to create a rule to allow connections on that port, but can't quite figure out how to limit this rule to only accept connections from the IP addresses I tell it to.
Having never seen these firewalls before, the interface is a bit overwhelming to look at and substantially different from the firewalls that I'm used to.
Any help is appreciated. Thank you!