Should the SMTP client provide the MTA with a globally resolved host name in HELO?

In short: I am trying to figure out if I should tell my friend-friend's postal administrator whether their mail configuration should be corrected, or if I have to revise my own policies in order to be more liberal in what I accept, or not.

A friend complained that he could not do anything on my mail server. I delved into it, and it seems that the host name provided by its mail server, when it connected to mine, was somewhere in the * .local space, that is, it was not globally resolvable.

They were rejected using the Helo command: Host not found; my postfix mail server. Perhaps I am strict on my UCE checks in postfix, so I turned on their (in my opinion, incorrectly configured) server, but now I am trying to find out to what extent they are actually incorrectly configured, or I'm just too harsh what I accept .

So I checked the RFCs - RFC 821 says: "The HELO receiver MAY verify that the HELO parameter really matches the IP address of the sender. However, the receiver MUST NOT refuse to receive the message, even if the sender of the HELO command does not check." which offers me that I'm really the one who violates the RFC.

Has this part of RFC 821 been replaced by a future RFC, what can I point out? Or should mail servers accept mail with fake HELO? Are there any respected authorities, I can point out that the HELO hostname must be valid, as a link to contact your mail administrator?

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Uh, I do not agree. He can provide general trash in EHLO / HELO if he wants. As long as he says something, and as long as I can resolve the ip address from which he comes from, I am happy.

Inside EHLO, there is often a short host name rather than a fully qualified domain name.

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Source: https://habr.com/ru/post/1697162/


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