Auto create alias rules in custom domain - regex

Hello,

I’m new to SimpleLogin. Our custom domain is configured, tested and it works. Are there some samples of regex expression publicly available or are there people willing to share the expressions they created?
I want to limit the auto creation of aliases to names that have a certain string at the end. mcdonalds@mydomain.com should not result in a new alias but mcdonaldsMyString@mydomain.com should result in a new alias.

Thanks.