Email Spams problem due to malware in some device in the network

RouterOS Beginner Basics
1

How can i set a firewall rule to allow only some devices to use the SMTP(587 port) protocol

2

Allow on Source Address List, with dst port 587, protocol 6 (tcp), on the forward chain. This should be sufficient information…

3

And how can i disable the port for everyone else

4

Add a drop rule on the forward chain that drops everything else:

add action=drop chain=forward

Make sure this rule is at the end of your rules.

I prefer the “allow specific traffic and drop everything else” way of thinking.