Linux is not susceptible to email viruses at all, because you have to download the attachment, and give it permission to run. (The same is probably true of Windows now.)

If you do that with an AV, you are playing Russian Roulette because there is no guarantee that any AV will detect the malware- more likely a Trojan than a virus.

Email attacks against Linux users are likely to be spear phishing attacks trying to get hold of banking passwords, in which case the attackers are likely to use a limited number of carefully crafted Trojan files that are not detected by AV programs.

To protect yourself against that scenario, you need to understand how social engineering is used in malware attacks and follow the rules I gave above.

An AV can give you a false sense of security.

There’s no reason you can’t scan suspicious email attachments with avast! (or send them to VirusTotal be be checked by a range of AV scanners).

I have been using email on Linux for five years without encountering a virus. I believe real time scanning is unnecessary, and a waste of computer resources, but if you still feel it’s necessary, there are AVs that provide it- for a price.