How to detect a spammer on a local network?

Question

Computer networks

How to detect a spammer on a local network?
The provider wrote spam from me, asked people who to spam, who has a virus computer, and he spam.
How to recognize a spammer through a router? on a computer (antiviruses, utilities)?
It is worth changing the Mikrotik router,

Answer 1

wiki.mikrotik.com — How to autodetect infected or spammer users and te...
Spam trojan detection with Mikrotik RouterOS
Blocking user's spam in Mikrotik is the most primitive option when the connection limit is exceeded, add it to the spam list. THAT is the normal user every 10-20 seconds does not send mail.

Answer 2

Torch ref. interface filter 25 port. TCP (default) from the IP from which requests are most often made is most likely infected.
Plus, the recommendation is to close the TCP port in the forward branch 25 for the time being.

Answer 3

Why is Wireshark bad?