Off topic: smtp HELO question

John Levine johnl at
Mon Mar 6 22:20:27 UTC 2017

This really should go to the mailop mailing list.

See and don't
be surprised if its TLS certificate is expired.

When you send mail, Thunderbird is doing submission, not SMTP.  They
are similar, but they are not the same.  Approximately 100% of
submission clients behind NATs put some random name or IP as the EHLO
name, and it doesn't matter.  That's not your problem.

>I do use TLS, but what I'm trying to debug is not so much that the email 
>service *I* use checks, but that the final receiving server scans 
>through the headers and flags anything with a NAT address.

That would be, to put it mildly, stupendously broken.  If they do
that, their false positive rate will be something like 50%, including
everything sent from Gmail.  It would be a good idea to check again
and see if perhaps they're doing something else and your problem is
something else.

John Levine, johnl at, Primary Perpetrator of "The Internet for Dummies",
Please consider the environment before reading this e-mail.

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