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Inbound email to SBS2008 Exchange not being received

Shannon Mollenhauer
Client's Exchange mail internally between users works fine. External senders trying to send mail to users are not getting through. System is on a Comcast cable internet connection with dynamic IP, so we use DYNDNS services. Ran MXToolbox SMTP check. Here are the results:

 Not an open relay.
 0 seconds - Good on Connection time
 10.265 seconds - Not good! on Transaction time
 OK - resolves to
 Warning - Reverse DNS does not match SMTP Banner

Session Transcript:
HELO please-read-policy.mxtoolbox.com
250 remote.designerconcepts.biz Hello [] [62 ms]
MAIL FROM: <supertool@mxtoolbox.com>
452 4.3.1 Insufficient system resources [5070 ms]
RCPT TO: <test@example.com>
503 5.5.2 Need mail command [5070 ms]
221 2.0.0 Service closing transmission channel [62 ms]

System has worked flawlessly for about 5 months. This just happened over the last 24-36 hours. What do I do?
Watch Question


In your event log do you have an event with an ID of 15002?

Distinguished Expert 2018

Insufficient system resources? Could be RAM, but almost every time I see that, it ends up being a full disk on the Exchange database partition.
Are any of your drives below 4GB? Also, is the server up to date on the lastest service packs?

Shannon MollenhauerProject Manager, Senior Technical Trainer


It was a disk space issue. Somehow my C: drive has accumulated way too many logs, temp files, etc. I followed the link you included and the link in the article about moving the Queue location. Got things restarted and mail is flowing. THANKS!