We have a problem with the email platform RoundCube.
This has nothing to do with roundcube.
We are reported to tha Abusix platform "https://app.abusix.com/lookup-and-delist?q=68.168.124.162"
Yep. Abusix is blocking you.
Why is this happening?
Abusix has banned your IP for "being bad".
How do we get rid of that error.
By contacting and dealing with Abusix.
SMTP error from remote mail server after initial connection: 550 5.7.1 [C16] RBL Restriction: See https://lookup.abusix.com/search?q=68.168.124.162
If you go to the link they gave you, it shows:
IP has been detected sending spam or is likely to be sending spam.
Intent: malicious
You will have to convince them why you should be unblocked after they flagged your IP as sending malicious spam.