SMTP ERROR

[vaidya]

While senting email I get the following error:

An unknown error has occurred. Account: 'qatarnet', Server: 'dtcoserv', Protocol: SMTP, Server Response: '421 SMTP Server Service not available or busy, closing transmission channel', Port: 25, Secure(SSL): No, Server Error: 421, Error Number: 0x800CCC67

This happens time to time, without any specific interval. When I do the maintenance in Wingate, it starts working.

I am using Wingate 5.2.2 (Build 892) with Windows NT 4.0 service pack 6

Can any body help ????????????