I hang out on the SourceForge-hosted inkscape-user mailing list, where I pick up useful tips for the Inkscape SVG editor (vector drawing program).
For months, the list has been plagued with spam; largely because anyone can send to the list. The policy has been not to require new users to sign up for the list before being able to send questions. This is commendably friendly and user-centric, but the spam has become a real annoyance.
One of the Inkscape developers finally said that, if a dozen or more people said "yes, restrict posting to list members only" and no-one opposed it, he would lock the list down. I attempted to vote yes and got the following rejection letter from SourceForge:
<firstname.lastname@example.org>: 184.108.40.206 does not like recipient. Remote host said: 550-Postmaster verification failed while checking <email@example.com> 550-Called: 220.127.116.11 550-Sent: RCPT TO:<firstname.lastname@example.org> 550-Response: 550 <email@example.com>: User unknown 550-Several RFCs state that you are required to have a postmaster 550-mailbox for each mail domain. This host does not accept mail 550-from domains whose servers reject the postmaster address. 550 Sender verify failed Giving up on 18.104.22.168.
Such irony! I had received a similar bounce a few days before from the FlexWiki-Users mailing list, which is also hosted by SourceForge, when I announced Vim Syntax Highlighting for FlexWiki.
I don’t own the reilly.org domain. It (and thousands of others) are owned by NetIdentity. I had an exchange with their postmaster, who said in part:
I did talk to sourceforge. They claimed it is an essential part of their spam filtering process to reject domains that dont have a postmaster mailbox.
I’ve tried that (at least on a test basis) myself and with all due respect to them, it is passe’ … doesnt work too well. And it has the added "advantage" of having to connect back to the sending mail domain every time to see if a postmaster for that domain exists. This holds up email and creates additional smtp connections - and hence even more load on mailservers, in the case of domains - with postmaster up and running - that are forged into spam.
I did suggest a few more rather efficient (and practical) filters they could use, but well, they didnt respond to those
He has since added a postmaster mailbox for reilly.org, so I can post to SourceForge lists again.
The Inkscape vote passed, of course. Only subscribers can post now. Non-subscribers can also use a webform to send questions, so it’s not a big impairment.