M was trying to send an email reply to someone for something related to school and the email bounced. Second attempt two days later, because there’s always the chance someone’s mailbox is overflowing and the mail-server gives an inconsistent reply, bounced as well. Meanwhile she received a phonecall from the person who wanted to know if M got the original email, since not everybody checks their email as often, so clearly the other person thinks the address is perfectly valid. Let’s have a look at what happens if I replay the SMTP manually:
$ telnet their.mail.server 25 Trying their.ip.num.ber... Connected to their.mail.server. Escape character is '^]'. 220 some.mail.server Mark's SMTP Server ready HELO my.host.name 250 some.mail.server MAIL FROM:<my@email.address> 250 OK RCPT TO:<someone@over.there> 550 User unknown 68.103.25.230 QUIT 221 some.mail.server closing session Connection closed by foreign host.
That’s odd, why is my ipaddress there? On a hunch, I tell our SMTP server to send email for this domain through our ISP and ask M to send it again. Lo and behold, it works this time, no bounce, and within minutes we even have a reply!
The hunch I had is that some.mail.server uses one of the DNS based Dynamic IP blocklists which means that it won’t accept email from addresses that are considered dialup, DSL, or cable ipaddresses. That’s fine, with the amount of spam going around I can forgive them for that and for this very reason I’ve got a series of domains where I know they use such a blocklist set up to go through my ISP, so that it arrives afte rall. But if you do this, could you at least have the bleeding decency to indicate this in the freaking error message? That’s there for a reason, you know? So that people like me can figure out what’s going on and adjust their setup instead of getting caught in the crossfire of the spam-wars. You don’t actually think spam software looks at what it says behind that 550 number, do you? (In fact, I’m pretty sure they ignore the result code altogether, given how dead addresses keep receiving attempts to deliver fresh spam day in day out.) With so many million messages being sent out, that’s about as likely as world peace.