I have found that Avast Free on my PC is letting emails containing a virus/spam through although Avast mobile is not
Can you give more details.
1. What is your email client, is it webmail or email program (thunderbird, etc.) ?
2. How do you know this, e.g. what did detect it ?
3. What was detected ?
4. If you are using a regular PC based email client and the regular Mail Shield, then I see nothing in the shield setting about Spam Detection.
5. If your email program is MS Outlook, that does have an anti-spam function, but you must be using the avast plugin for MS Outlook.
Hopefully you can see we need more information.