Found that outgoing mails not successfully in Exchange 2010 server

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?

thanks,
MezzutOzilAsked:
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spiderwilk007Commented:
You must configure a reverse DNS record for the domain name called a PTR record. This record is not controlled by your DNS it has to be setup with the ISP. Some organizations will not accept mail if no reverse DNS exists.

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MezzutOzilAuthor Commented:
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