I am a user of the Home edition of ClearOS, which means that my ISP is one of the many residential internet service providers. Spectrum, AT&T, etc. all provide dynamic IPs with dynamically generated hostnames for those IPs for the purposes of reverse DNS lookups. On Spectrum/Time Warner, a reverse DNS lookup would result in cpe-xxx.xxx.xxx.xxx.nc.res.rr.com, and for AT&T it is xxx.xxx.xxx.xxx.lightspeed.rlghnc.sbcglobal.net. In order to provide a valid response to other email systems that do a reverse DNS lookup, I need to keep the hostname in /etc/postfix/main.cf set to whatever value my ISP keeps for my IP. Is there a way to automatically update postfix when dynamic DNS does an update?
In Dynamic DNS
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I don't think it is really needed. Normally it is only the existence of a reverse DNS name that it is checked as an anti-spam measure and not that it matches the host name. Postfix can check that it exists and is valid but it is not recommended. It would even catch out major players who round-robin their mail servers (thing G-mail, Office365 etc)
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