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depontius
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PostPosted: Thu Nov 03, 2016 5:48 pm    Post subject: Mail routing observation and question Reply with quote

This is only marginally Gentoo-related, in that my Gentoo server is part of this flow. However there is also some interesting information here, which people might be interested in reading and understanding. So while my question doesn't rise to the level of posting to the Gentoo Forums, the interesting and educational nature I believe does.

I have a vanity domain, registered at DynDNS.com. I guess that alone makes me an old-timer, because it sounds like they serve primarily businesses these days, and most individuals go elsewhere for domains. When I was looking to "connect" my new email provider to my domain, they didn't even list DynDNS. It seems like long ago, DynDNS was the only game in town for mere people.

I also have an unsatisfactory email provider. I had DynDNS pointing my A-record to that provider's server, where I had an account. There was also an MX record pointing to my A-record, which pointed to their server. They provide much more than email, but email is all I have been using.

After getting fed up, I found a new email provider. However they are (currently) providing only email to me, so I only changed my MX records to point to their server.

After the change, my mail started coming through the new server. In my /etc/fetchmailrc I simply added the new server, and kept fetching from the old, for some crossover time. However something odd has happened. I was thinking "crossover" meant a few hours, while TTL expired. However several days later, I'm still getting email through the old account. But as near as I can tell, everything coming over the old path is spam. There's a little bit of spam coming over the new path, but far more over the old.

So it seems to me that the spammers are ignoring the MX record and going straight to the SMTP (or one of the alternates) port on the machine pointed to by my A record. A quick search indicates that this seems to have become common practice.

So here's the question: Can I set my A record to 127.0.0.1? It seems like a fun and obvious thing to try, but it prompts the question, "What can possibly go wrong?" Is there a better blackhole address than loopback? I like loopback here, because I like the idea of aiming the spammers' guns at themselves.
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szatox
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PostPosted: Thu Nov 03, 2016 8:55 pm    Post subject: Reply with quote

:lol:
Isn't MX supposed to point to email server's name rather than it's IP directly?
I mean, you're gonna need an A record for your email server anyway... You can set a wildcard target and point this one to localhost though.
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depontius
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PostPosted: Thu Nov 03, 2016 10:07 pm    Post subject: Reply with quote

Yes, at DynDNS the A record for my domain name points to the old server's IP. With the old mail provider, the MX record pointed to my domain name.

For the new email provider, they only gave me a primary and secondary MX hosts for the MX records. Effectively, my A record is not needed, at this point. It probably won't be needed until I get some sort of website. That's what makes me want to point my A record at loopback. If spammers are going to mail to the A record, let them spam themselves.
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