421 Service Temporarily Unavailable issue from domain modianotv.com (62.38.205.225)

Hello,

I am the administrator of modianotv.com mail server running behind a public ip of 62.38.205.225

Recently two of our major customers failed to receive our company emails.

They are both using messagelabs.com services.

After looking at the SMTP server log files, we came accross the issue of 

216.82.251.230 OutboundConnectionResponse SMTPSVC1 OLYMPOS - 25 - - 421+Service+Temporarily+Unavailable 0 0 35 0 1219 SMTP

Please advice what can be the source of such an issue and if there was a penalty at this IP, please remove it from your databases.

thanks in advance

Dimitris Tsichles