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DNS mystery

By Net Designer ·
Originally we had the following configuration for our e-mail system: domain1.com and domain2.com where pointing their MX records to our router1. Later we noticed that there were too many e-mails coming to non-existing accounts for domain1.com and here is what we did. We set up a Linux Sendmail server, created aliases for domain1.com that would point to domain2.com (e.g. "aliases" file: user@domain1.com: user@domain2.com). We also put this Linux box behind router2 and re-directed domain1.com's MX record to router2. Now, theoretically any mail for domain1.com has to go to router2 and be forwarded if a record exists in "aliases" file and dropped if it did not. It works fine for legitimate mails. However, we are still getting e-mails for non-existing users for domain1 and they go directly to router1, as if someone has statically assigned resolution of domain1.com to original router1. I get response from router2 when I ping domain1.com, so it is kind of a mystery that has no explanation.

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by BFilmFan In reply to DNS mystery

MX records are sometimes listed all over the Internet. If you run a check from the Internet-side of the router, and ping your MX records what IP addresses are being returned? You should be able to run this check from home or if you have an ISP conenction from there.

When you said you set up a Sendmail server for domain 1, what was your other email system? If it was Exchange and domain 1 is the primary domain, the Exchange server has to be primary for that domain and this explains why mail is behavign strangely.

I would recommend you set up a SPAM filter and when spammed, let that software or appliance handle the issue.

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by Net Designer In reply to

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by Net Designer In reply to DNS mystery

I'll try pinging from Internet side to mail.domain1.com but don't think that anything but router2 would reply, as A-record points to it properly and any legitimate mail comes to router2 first and then forwarded to domain2.
As far as original configuration, both domain1 and domain2 were sitting on GW6 with domain2 being primary. Domain1 was removed from GWIA configuration after it was moved to Sendmail. Nothing-nothing points domain1 to router1 - that's why it's so strange why SPAM-only mail for domain1 goes to router1. Except your first thought that MX records are all over and still may exist the one that points to router1, I really have no answer.

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by Net Designer In reply to DNS mystery

FYI: mail.domain1.com pings to router2 from outside the LAN, just as designed. I guess, there are old MX records floating around at SPAMmers sites, as only SPAM goes directly to router1.

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by Net Designer In reply to DNS mystery

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