Sent emails appear in the mailbox queue attempting to "retry". After 24 hours a message is sent to the internal sender saying, that is still trying to send. in 48 hours the message fails. This is happening on about 10% of our email and it is happening to the same domains. 90% of the email is being sent properly. I've checked blacklists repetedly and mxtoolbox says I'm ok with the exception of the diagnostics which says, "Warning - Reverse DNS does not match SMTP Banner".
This problem started 4/8/10
thanks for your help.