On Tue, Apr 18, 2023 at 10:19:58AM +0800, tom--- via Postfix-users wrote:
> I saw many peer MTA connecting me with this default HELO hostname:
> localhost.localdomain.
>
> Is this a FQDN?
Yes, it is a fully-qualified domain name.
> Is it valid?
Depends on your perspective. This FQDN does not exist in the global DNS
(there is no "localdomain" TLD delegated in the root zone). This sort
of name is typical for MUAs, and not typical of well run MTAs. Whether
this sort of name is sufficient grounds to deny access is less obvious.
If this is not a significant fraction of your unwanted mail, the filter
may not be worth the risk of blocking something misguided, but useful.
--
Viktor.
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