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I would like to operate an incoming-only MDA (Mail Delivery Agent) server mail for domain xyz.com on an Ubuntu server hosted behind my ISP (Internet service provider) Comcast. The objective is to receive aaa@xyz.com and potentially reject (not bounce) spams. I don't intend to have any SMTP server on this machine.

Reverse DNS for Comcast gives me: c-XXX-XXX-XXX-XXXX.hsd1.ca.comcast.net and I guess that as a home user, I will never be able to point this reverse DNS to the domain name.

http://whatismyipaddress.com/blacklist-check reports all OK for this IP address except one for spamhaus.org. IP is listed in PBL as explained here: http://www.spamhaus.org/pbl/query/PBL1523090. I have understood that it's not a catastrophic situation and it can be fixed.

Question: is this a problem to have a reverse DNS pointing to a domain address that is different from the domain for which the mail server is operating? Would some SMTP server refuse to send email to my MDA because of that?

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migrated from serverfault.com Aug 13 '13 at 21:53

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How do you intend to accept mails without running SMTP? Also, RBLs and DNS checks are rarely if ever applied to egress mail; they are for filtering spam on ingress. –  Falcon Momot Aug 13 '13 at 21:53
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You can't receive mail for some domain xyz.com with MDA only, you need to run some MTA somewhere which will accept incoming mail with SMTP protocol. And usually nobody cares whether receiving end of SMTP transaction has correct reverse DNS records or not.

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also you need not worry about your PTR records when you only want to receive mail. Reverse DNS lookup will be done only when you send out mail from your server. –  clement Aug 13 '13 at 19:13
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