Basic SMTP firewall

[JonathanC]

Hi,

I've got a few sites on which a PC sends on SMTP to our Microsoft 365 mail relay.
These are just outgoing for alarms.
What is the best way to block all SMTP traffic  except for the one computer? 

Just layer 3 firewall and allowing from just 1 internal IP, then putting a rule block everything else?

Thanks

[KarstenI · Accepted solution]

Yes, that is the way to go:

1) Allow IP1 -> Server:25/465

2) Deny any -> any:25/465