=> Please let us know if the username you were trying to register contained UTF-8 characters or not so that we would know if this was the cause of the problem or not.

I tried to create lizabelos with a CNRS (didn't worked) and a GMail account (worked). I tried to create lizab with a lix account (didn't worked). Another person of my lab tried the same.

I don't see any pending accounts for either of those email addresses.
What account name were you attempting to register?

The root cause of that error is use of UTF-8 characters in any of the
email headers then requires an SMTP UTF-8 transfer protocol.  Which
indicates to me that a header in the email included a UTF-8
character.  I can only guess that this must have been due to a UTF-8
character in the username.

I don't know if UTF-8 user names are supported or not.  Given the
information so far I would guess not.  But perhaps that would be a
feature enhancement. Please let us know if the username you were trying to register contained UTF-8 characters or not so that we would know if this was the cause of the problem or not.

Hidden courriel domains are cnrs . fr and lix . polytechnique . fr