Exchange 2010 - 400 4.4.7 error

[Iain.Faulkner]

Morning all,

 

Seem to be having a problem with our Exchange server. Essentially we have a long list of email sat in a queue unable to send all with the error code 400 4.4.7.

 

Having done some quick research into it, most suggestions are that the emails are being sent to a domain which cannot accept them, however there is a large number of different domains that I can see (certainly over 50) so I find it hard to believe that all these domains cannot receive email from us.

 

We are receiving emails into school, it is only sending them back out again where the problem lies.

 

I'd post a screenshot, but we've just cleared out the queue to see if that helps anything....as soon as the error regenerates I'll post one.

 

Any help anyone can give us would be gratefully received.

 

Thanks

 

Iain

[AngryTechnician]

Have you checked spamhaus to see if your IP has been blacklisted? That could account for more than one domain rejecting mail from you, though normally with a different error code. Worth checking just in case though.

[Iain.Faulkner]

Thanks for that, just checked it and we're not on any blacklist according to spamhaus

[Iain.Faulkner]

This has now evolved slightly,

 

Within the queue viewer, on the smtp queue we have another error under "last error", see below

 

451 4.4.0 Primary Target IP address responded with: "535 5.7.0 Error: authentication failed: authentication failure." Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate host

 

Any suggestions?

[Iain.Faulkner]

Right, this appears to have been resolved.

 

Although not 100% sure on what it was that has fixed it, we spoke to the company who do our email redirection and within 20 minutes external email is being sent again......we did make one slight change to our DNS as well, but only physically adding the internal DNS addresses...I know where my money lies as to where the problem was.