question

StefanFI-2065 avatar image
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StefanFI-2065 asked StefanFI-2065 commented

MS365 Exchange doesnt conform to RFC at smtpin

I just checked a postfix configuration at a customer.
Resp. postfix is configured incomplete, so it sends localhost / 127.0.0.1 at EHLO to outlook.com (no authentication).
This does not conform with RFC, which requires FQDN in EHLO.
Any other ISP rejects the connection, why does MS365 allow and accepts mail?

Has anything to be configured in MS365 admin?

office-exchange-server-administration
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AndyDavid avatar image
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AndyDavid answered StefanFI-2065 commented

No, sorry not possible. That would be a setting at the server level and we have no access to that.

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Means I can install an MTA anywhere and SPAM as I like ...

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AndyDavid avatar image
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AndyDavid answered StefanFI-2065 commented

What RFC requires the FQDN in the EHLO?

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2821, in words:

https://datatracker.ietf.org/doc/html/rfc2821#section-4.1.1.1

4.1.1.1 Extended HELLO (EHLO) or HELLO (HELO)

These commands are used to identify the SMTP client to the SMTP
server. The argument field contains the fully-qualified domain name
of the SMTP client if one is available.

and, generally ISPs reject connections without like this:

"Recipient address rejected: Mail appeared to be SPAM or forged. Ask your Mail/DNS
-Administrator to correct HELO and DNS MX settings or to get removed from DNSBLs; MTA helo: localhost, MTA hostname: unknown"
or
"550 Please use a fully-qualified domain name for HELO/EHLO (in reply to MAIL FROM command))"

MS365 is the first I see who doesnt.

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Yea, but I dont see that its required :)

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OK, agree in some way :-p, but my question remains: CAN I configure MS365 so that it will require?

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