I have several Exchange 2003 servers (all independent and not same organizations or domains) that have been configured and working perfectly for years. No changes, with the exception of MS updates, have been made. Over the past few months, the increase of the 4.4.7 failed to deliver has increased substantially on all servers. I have checked the DNS, the black list servers (54 of them to make sure not listed) and have found no errors or changes to my servers, all past all test including DNSSTUFF (all DNS and Mail) etc. The really strange part is that the same (exact same) mail (when testing) will sometimes go through and sometimes generate the NDR. While I know the generic answer for this message is to check the servers on the other end, this occurs on some fortune 400 level receiving servers and I have trouble believing (especially with the sometimes work and sometimes not) that the problem is misconfiguration on the other end. Also, this sometimes occurs between my customer and my server and I control both ends and both ends pass all test. We will send a large number of emails back and forth and everything will be fine and then all of a sudden one fails with the 4.4.7. Is anyone else seeing an increase on these "delays" and has anyone got any theories as to what is occuring and a method of troubleshooting this? Thanks in advance to anyone who has suggestions!

Usaully 4.4.7 ndr code is due to a greylisted system used from the recipient's antispam. you can try to ask them for this...

Hi, Message expired. Message wait time in queue exceeds limit, potentially due to remote server being unavailable. make sure the domains you are trying to sent mail too, are valid domains, they do exist. When mail server sends out mail to another SMTP domain (mail Server), in a very basic way the errors are related to either your mail server or the destination mail servers. For instance if I am trying to send mail to you and , your mail server is not liking something ( My mail server is missing PTR record, or my mail server is listed in RBL ( real time block list) list, I am sending spam mails, my MX record is missing etc. Mail servers will sent mail with expectation of destination mail servers are going to accept them. During this process many things might have gone wrong, might cause message to delay or never made it to destination. These type of issues , the destination mail server will either reject or slow down the mails. Simple telnet test can give you much better information and you will need to perform troubleshooting to figure out where the culprit is. Try sending mail from command line to one of these servers to see what will be the response?Please remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread. Thanks Gen Lin-MSFT