SOME External emails are staying in the message queue 1

[mingtmak]

Single exchange server acting as all roles.
Most emails going out. The ones not going out are giving the error:

451 4.4.0 Primary Target IP address responded with "421 4.2.1 unable to connect".

I've tried telnetting to some of the failed sends and get the "...could not open connection to the host, on port 25: connect failed"

nslookups for mx records of failed sending domains are bringing up the correct smtp servers.

I've tried changing DNS servers.
I've set the fgdn of the send connector.
Firewall seems to be set correctly.

can anyone offer assistance to this?

- Jon

 

[ShackDaddy]

Either the target servers are down, or their anti-spam measures are implementing connection dropping against your IP or IP block. Jump to a server at a different site and try the telnet test again. If it still fails, then the server may be down, if it succeeds, then you're dealing with connection dropping/blocking.

You could also run DNSStuff's DNS tool against that domain name and see what the report looks like.

Dave Shackelford
Shackelford Consulting

 

[bTkalternate]

Go to

http://www.mxtoolbox.com/index.aspx

and use their online diag tool. Should help you out in no time.

 

[mingtmak]

HA! The IP that the ISP provided were failing at a certain hop, whereas another of theirs wasn't.

Thanks guys! The Telnetting from multiple locations helped a lot. I assumed too much when I didn't consider the ISP being at fault.

- Jon

 

[Zelandakh]

ISPs are normally at fault!

 

[58sniper]

Agreed. The fact that you got an error when telnetting means the problem's not on your side (assumptions being that you're attempting to connect to the primary MX record).

Pat Richard MVP
Plan for performance, and capacity takes care of itself. Plan for capacity, and suffer poor performance.

http://www.ucblogs.net/blogs/exchange/

 

[mingtmak]

No doubt, that was the 2nd time an ISPs mismanage of IP addressing has caused issues.

Last time, the ISP provided already assigned IPs to another customer. For us, I couldn't test the VPN connectivity w/o it failing, for the other client I imagine their internet was going down.

- Jon

 

[Zelandakh]

Even when an ISP documents their changes, the guy who does the actual implementation can still mistype - it all ends up on one person's shoulders.