Quote:

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Outlook "HELO/EHLO"-Bug

The HELO command is defined in RfC 821 as "HELO <SP> <domain>". The term of domain is defined to what's widely used today, saying for example "Whenever domain names are used in SMTP only the official names are used, the use of nicknames or aliases is not allowed". Keep in mind that the internet was somehow different in 1982 when this RfC was written.

If the client can't figure out his official name (for example when he is behind a NAT gateway) he should use an address literal (e.g. [192.168.2.42]). Outlook doesn't care, it just always send's the computers nickname. That's why you find often things like OEMCOMPUTER in this place.

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code:
 NOQUEUE: reject: RCPT from unknown[1.2.3.4]: 504 5.5.2 <COMPUTERNAME>: Helo command rejected: need fully-qualified hostname; from=<smth@example.com> to=<smth@example.com> proto=ESMTP helo=<COMPUTERNAME>