Install clamsmtp by entering the following commands in the terminal:
sudo apt update sudo apt install clamsmtp
Description:
virus-scanning SMTP proxy
ClamSMTP is an SMTP proxy daemon that checks for viruses using the ClamAV anti-virus software. It can act as a traditional SMTP proxy with publicly accessible ports or as a transparent proxy, where SMTP traffic is redirected to the ClamSMTP by your router. . ClamSMTP aims to be lightweight, reliable, and simple rather than have a myriad of options. It is written in C without major dependencies. ClamSMTP does not do general spam filtering, it only scans for viruses. . You do not need a local mail-transport-agent installed, since this server can forward to a remote one.
Homepage: http://thewalter.net/stef/software/clamsmtp/
Version: 1.10-17ubuntu1
Section: universe/mail