That mismatch between DMARC verification domain and the domain of the “from” header is called DMARC Alignment. Any modern spam filter is going to mark unaligned messages as spam. Especially if one of the domains is completely non-routable like .onion.

And even if you sent the email and it got through with your .onion address, no one would be able to reply to you because the replying mail server can’t even look up the MX record for your .onion domain.

TL;DR you can send emails from .onion addresses if you want, but no clearnet server is going to accept them.

So when you send an email, you can actually put whatever you want in the from header. I could send an email that says from “made.this.up@website.doesnotexist”. The protocol doesn’t care.

Do you know who does care? The email server you’re sending messages to, because spammers and scammers love to try and send email with fake from addresses.

So, there’s an entire verification system in place that involves looking up public keys from the website that the email claims to be from. (this is a gross over simplification. Look up SPF, DKIM, and DMARC for more info). The problem is you can’t even reach .onion sites from the clearnet to do the lookups. So no email servers would be able to validate your address is legitimate and so would drop it as spam.

All words you spell must include the central letter, adjacency doesn’t matter.

The design is a bit of a visual joke combining the concept of a “spelling bee” competition with the honeycombs of literal bees.

Losing my religion

None of these words are in the Bible

You should definitely set up a DMARC record to prevent other people from using your email domain to send spam. If you don’t have DMARC configured, other email servers will give any senders the benefit of the doubt and accept mail that claims to be from your domain.

You can just set the DMARC record to reject 100% of unverified mail and call it a day. Since you aren’t sending anything it won’t affect you.

According to all known laws of aviation, there is no way that Dumbo should be able to fly. Its ears are too small to get its fat little body off the ground. Dumbo, of course, flies anyway. Because Dumbo doesn’t care what you think is impossible.