Linux Mint specifically excludes the snap store due to the many criticisms people have already mentioned here. Doc refers to version 20, but I believe it's still the same in the current version. Not sure about other ubuntu-based distros though.
https://linuxmint-user-guide.readthedocs.io/en/latest/snap.html
Look up the instructions for your mail provider to set up SPF, DKIM, and DMARC records in your DNS so email services know which emails sent from your domain are actually legit. Without those records telling email servers what's valid and how to handle what's not, it's basically the Spiderman pointing at Spiderman meme.
https://www.namecheap.com/support/knowledgebase/article.aspx/317/2237/how-do-i-add-txtspfdkimdmarc-records-for-my-domain/