Recently, Meredith discovered that her emails to Peter, one of her best friends from Yale and now a grad student at the University of Michigan, were being bounced. The error messages looked like this:
host truecrime.mr.itd.umich.edu [141.211.125.42]: 553
5.3.0 No access from your host
All of our email is relayed through a mail server that's run on a server in our home. The server is running 24/7, connected to the PacBell DSL line. It is NOT an open relay. Despite daily attempts by spammers to use the server to relay their spam, to date, exactly zero attempts have been successful. Nice try; now go away.
So why was our email being blocked? After emailing postmaster@umich.edu -- no easy task, since I had to find another server to relay the mail through -- they replied that they were getting a lot of spam from another server at one specific IP address connected via PacBell's DSL, so blocked all addresses that resolved as *.dsl.snfc21.pacbell.net. This basically covers all of the Bay Area. Surely, I suggested, they could choose to block just the offending address, and not ALL of the Bay Area. At any rate, they removed the block, but warned that if they start getting spam from the other machine, they'd put the block back on.
And, sure enough, email yesterday bounced -- No access from your host.
Sigh.