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There is no proper single article or I haven't researched properly, to find what does matters most for MTA's reputation IP or the hostname of the MTA or both matters equally. I am asking this question because I am facing a situation, where I am changing my hosting of prod servers, which require changing the public IPs of the platforms and MTAs, so for the updated IPs of platform, I need to inform clients through my whitelisting page, so that they can update their network for our IPs. But for mail servers there's one more thing, that is the IPs should be warmed up to use it in production so that it can send emails in large numbers.

So, my question is, if I create new MTAs with the same existing hostnames but of course the IPs would be different, will it require warming or it is good to go live. and whether the IP or hostname is warmed up or not, where does this affects? just only the public email providers like yahoo, google, outlook, etc. or does this affects the private MTAs of some clients too.

one more thing, I have seen many RBLs they just show reputation based on only IPs but the hostname, so is it, that only the IPs reputation matters, and that I would have to warm up my new MTAs with new IPs?

some clearance on this would be of great help thanks!

Anil Bind
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Basically SMTP require your hostname and IP being resolved properly and this requirement is checked during connect and HELO phase of any connection. Your hostname (which is delivered to other party via HELO) should have DNS A record with the address your MTA is connecting from. And this IP address should have PTR record leading to this hostname as well. Other party MTA will not trust your hostname if one of those checks have failed.

So the answer is yes - you can prepare DNS records and wait they distribute across internet and your MTA can go live.

Although, there are some other checks like SPF domain records which should allow your MTA sending e-mails from specified domain, this should be checked too.

As for RBL question - most of RBLs have their databases build about IP's, not domainnames or hostnames. The only thing you have to do here is to check new IP address history and you can use it immediately if the history is clean.

kab00m
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  • Thanks allot @kab00m, – Anil Bind Oct 13 '20 at 07:56
  • but whom does the warming of the IP affects, like public email providers – Anil Bind Oct 13 '20 at 07:58
  • In common it will affect any server sending e-mails to your domain. Not every MTA in the world conform to standards in the same way so it is barely predictable which service will be affected. The standard says your DNS should be fine. Any MTA will reject sending mail to your new server if it is not fine. They will retry delivery when DNS records would be cleaned up. World MTA would re-request your DNS records after they expire and this time is set in TTL record of your DNS zone. – kab00m Oct 15 '20 at 19:33