Juba007 This extension allows you to whitelist or blacklist custom email adresses by domain or regex: https://flarum.org/extension/clarkwinkelmann/flarum-ext-email-whitelist If you mean disposable emails (like 001gmail.com) you can use this extension: https://flarum.org/extension/fof/disposable-emails
luceos Walys what you imply is sub addressing: https://en.wikipedia.org/wiki/Email_address#Sub-addressing This could be done with a local extender as well as a little extension. Don't currently have the time to write the code for it though.
clarkwinkelmann As suggested by Juba007 my email whitelist extension should work here, you just need to craft the right regex
