Hi guys;

This evening my Exchange 2010 server started queuing external mail on queue viewer, it is connected to a Smarthost (smtp.managedapps.co.uk) for external emails
all internal mail and external email coming in are ok.

So I restarted the Transport service, same issue.

Sadly My ISP has closed since I found the issue out later in the evening

I tried telnetting smtp.managedapps.co.uk on port 25 and get no connection

Disturbingly when I went to the www.managedapps.co.uk website it was down

Waited a while and it looks like website is backup again and I could telnet the smarthost.

Although restarting the transport service again to try, all external emails are still stuck in outgoing queue with this error:

451 4.4.0 primary target ip address responded with 421 4.4.2 connection dropped due to socket error

Is this still ISP end issue or is there anything I could do ?

Thanks as always