Issue Sending Mail Suspended after changing outgoing IP?

[yabado]

Server operating system version

CentOS Linux 7.9.2009 (Core)

Plesk version and microupdate number

Version 18.0.47 Update #5, last updated on Oct 26, 2022 03:17 AM

So Microslop has blocked my server and I need to send from a different IP.

I create the IP and set up it's reverse DNS. All good.

When I add this new IP as the Outgoing Mail IP, all mail stops sending. Below is the error ...

Nov 12 07:22:53 panel postfix/error[30441]: D450A262495B3: to=<[email protected]>, orig_to=<[email protected]>, relay=none, delay=0.72, delays=0.72/0/0/0, dsn=4.4.2, status=deferred (delivery temporarily suspended: lost connection with 127.0.0.1[127.0.0.1] while receiving the initial server greeting)

If I go back to the original IP, then email starts flowing again.

What am I missing?

I have tried all the suggestions I could find in the docs with no success.

TIA