Why, off hand, would anyone block an email _receiver_… from a quick glance at the server code, this project is essentially an SMTP dead end; any mail sent to it is temporarily stored in the database, then periodically flushed. With no sending or forwarding of mail to other servers, and assuming it’s properly acknowledging receipt, why would anyone else block it?
Or get a cheap domain and setup a catchall email forwarding to a private box. If you want an anonymous domain, checkout https://kycnot.me/services#VPS.