From my devnullius gmail.com I started to receive these errors more and more:
504 5.5.2 <pdev10>: Helo command rejected: need fully-qualified hostname
It's not very often, but often enough.
At first, I blamed it on other email servers but today I sent an email to someone, got a reply, replied to it and 504 5.5.2

A fresh email to the same email address also returned this

I have no idea where to look for it. I just log in to devnullius account and do my thing. Google does not show much relevance either...
Anyone an idea? *any* idea?

Devvie