Mailserver block the requests that are used to get a list of inboxes ("accounts")
many servers will block mailservers that are not on an allowlist
many servers will block servers, if mails were sent to nonexistent addresses a couple of times
the message "recipient not known" will not appear often, as servers may "black hole" a senders mail and cut off the connection without sending the status message back

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[–] Max_P@lemmy.max-p.me 9 points 4 months ago (1 children)

On top of everything the others have said, another way this isn't possible reliably is servers that just accept all email and forward it to a catchall address.

Some also have trap addresses where sending email to it will result in putting that address directly into the spam filter and everything coming from it feeds into training the spam filter. I'm an individual, not a company, so all the common IT, HR, support, press, sales, whatever addresses are traps.

When websites force me to enter an email, I enter one of the traps so everything they send me and everyone they share that email with gets the banhammer instantly, and I can track which asshole website did that to me as well.

[–] boredsquirrel@slrpnk.net 1 points 4 months ago

Very smart. Learned something.

Many many company mains are standard, which is interesting as they will get tons of spam.

But makes sense that this is not a good way, that the tools for scanning for available addresses are blocked and that there are even honeypots.