This is using MS Exchange 2010 server in 2008 r2 AD Domain. Recently, found that sometimes outgoing mails may failed. I checked from the queue viewer, that are always few mails in queue with retry state. Most of them having the error as follows:
Last Error: 421 4.4.2 Connection dropped due to socketError
Last Error: 421 mail.recipient.com Error: timeout exceeded
Incoming mails are working fine. Why these outoging mails failed?