How do I blacklist a contact from a list,

[tanya]

If you don't want to send email to him/her, make his/her email address opted out.
If you don't want to receive emails from this contact, add email filter

https://www.espocrm.com/documentation/user-guide/emails/#user-content-email-filters

[Portia]

I'm just wondering how I can blacklist a contact from the system, so that they no longer receive any further email when I mass-mail out.

Thanks.