> Which suggests that your end (on an RFC1918 IP address of 172.17.25.35)
> is behind a NAT firewall, which could part of the problem. The
> SMTP server however does not seem to be reachable from Internet at
> large, so the networking topology here is unclear.
Indeed, only our servers are able to reach this MX. This is the normal
behavior.
> There we have it, the EHLO response omits the first vanity line,
> and so SIZE becomes the vanity line, and is ignored.
This is it! Thanks for the information, I was not aware of this RFC subtlety.
We’ll reach out to the owner of the MX to see if he can change this behavior.
> This response must follow ".", and the server must not switch back
> to command-mode until that happens. Just hanging up can cause
> problems. Mind you, when the connection is lost mid-transfer,
> Postfix will attempt to read any pending premature response
> from the server (since Postfix 2.4, 11 years ago):
Another RFC breach that we will notify to the postmaster.
Many thanks for the time you all spent on this issue. Your help was precious on
this one.
Florian
