Github dislikes email “aliases” so much that they will shadow ban your otherwise normal activities for months, and once flagged, support will request not only a “valid” email domain but also that you remove the “alias” email from the account completely.
I had the same issue with my Anonaddy alias, I just made an alias using my domain name and works fine now. It’s unfortunate that so many project are on shithub.
I gave them an generic “alias” through a more mainstream service than silomails, we’ll see if that pacifies them.
Same experience here