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I have an email server which sends email for multiple websites (different domain names each)

the reply-to will correspond to no-reply@website-a.com (or whatever their username/website is) but the return-path will always correspond to a single address that is common for all websites ie: bounce@web-host.com.

I understand that rDNS needs to work in order for my email to achieve maximum deliverability, but does rDNS need to correspond to the reply-to or the return-path or both?

Thank you!

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1 Answer 1

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rDNS does not need to relate to the the reply-to or return-path. Both these addresses should be valid addresses.

Correct rDNS for mail.example.com with address 192.0.2.5 would have:

  • a PTR record for 192.0.2.5 pointing to mail.example.com,
  • an A record for mail.example.com having an address of 192.0.2.5, and
  • optionally a SPF TXT record for mail.example.com containing "v=spf1 a -all".

Your mail server should be configured to identify itself in the HELO command as mail.example.com, not example.com or mail.

If the domains you send mail for have an SPF record, they should allow your host to send email for the domain. I do recommend that they have an SPF record. I recently did a posting on Securing your Email Reputation with SPF.

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so the rDNS needs to correspond to the domain given in HELO? The A records for the domains given in HELO do not necesarily correlate to the ip of the interface used to send the mail (because the websites themselves only have one ip each, however the email server may have more than one ip per website it is serving) is this something that will flag me as spam? If so, I can do something like send email-a.website-a.com in HELO so that the rDNS and A records match, but if that is not necesary I'd rather not send a subdomain in the HELO. I do use SPF, thank you for the suggestion though. –  radmilla mustafa Mar 22 '11 at 21:54
    
Yes, rDNS is used to verify whether your server really is gmail.com when you say it is. (gmail.com is one of several frequently forged addresses used in HELO commands. The actual server names gmail uses are different.) Do use a subdomain for your mail server's address. Having a records for example.com, and mail.example.com returning the same address is valid and common. The PTR record should point to your subdomain. Using a domain as the mail server's HELO name is a marker that you are sending Spam. –  BillThor Mar 22 '11 at 21:59
    
That's correct. –  Hyppy Mar 22 '11 at 21:59
    
You should be able to configure your mail server to bind to only one Internet address. This makes configuration simpler as you only need to configure the DNS PTR for one address. –  BillThor Mar 22 '11 at 22:06
    
Ahh that makes sense, so I will need to send subdomains in the HELO. My only gripe with that is that I will need to add a TXT record for the spf for each subdomain, which is ok (laziness was my reason for wanting to avoid subdomains.) One more question (again, this is the result of laziness) would I be flagged if let's say one of the subdomains had 3 or 4 different A records, the ip itself would of course only have one rDNS. So to speak, each subdomain would have the same set of As and each ip would have 1 PTR –  radmilla mustafa Mar 22 '11 at 22:10

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