I love Gmail, but I hate this thing about it:

I accidentally used the Gmail SMTP server to post my two last messages
to ACF, and Gmail substituted my Gmail username, "kikizas", for my
diplay name, "Demetris".

This is something I have seen and read about before, and it seems to be
an undocumented policy of Gmail (I can find no mention of it in the
Gmail help pages). It is not completely unjustified, as far as I
understand, but at least it should be stated conspicuously.

I can imagine situations when this substitution can get you in real trouble.

Greetings
Demetris (not using the Gmail SMTP server)