We are getting sporadic 500 5.5.1 errors when sending to one particular domain. 99% of the mail goes through fine, the other 1% gets kicked back immediately with the following error:

08:27:33 008 MSG 2931076 File: /groupwise/dom/gwiadom1/wpgate/gwia1/wpcsout/gwif3c2/4/4c8f31ef.JJ0 Message Id: (4C8F31E7.C1C:41:49610) Size: 6.9 Mb
08:27:33 008 MSG 2931076 Sender: user@NorthMemorial.com
08:27:33 008 MSG 2931076 Converting message to MIME: /groupwise/dom/gwiadom1/wpgate/gwia1/send/xc8f31f5.459
08:27:33 008 MSG 2931076 Recipient: user01@umn.edu
08:27:33 008 MSG 2931076 Queuing message to daemon: /groupwise/dom/gwiadom1/wpgate/gwia1/send/sc8f31f5.459
08:27:33 392 DMN: MSG 2931076 Attempting to connect to mhub-w.tc.umn.edu
08:27:34 392 DMN: MSG 2931076 Connected to [134.84.119.108] (mhub-w.tc.umn.edu)
08:27:34 392 DMN: MSG 2931076 Send Failure: 500 5.5.1 Command unrecognized: "MAILXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXXXXXXXXXXXX
08:27:34 392 DMN: MSG 2931076 SMTP session ended: [134.84.119.108] (mhub-w.tc.umn.edu)

However, an hour later, when I send a test to the same user, no problem:
09:35:38 856 MSG 2934573 File: /groupwise/dom/gwiadom1/wpgate/gwia1/wpcsout/gwif3c2/4/4c8f41e5.E20 Message Id: (4C8F8833.6D9:238:53082) Size: 1.7 Kb
09:35:38 856 MSG 2934573 Sender: me@NorthMemorial.com
09:35:38 856 MSG 2934573 Converting message to MIME: /groupwise/dom/gwiadom1/wpgate/gwia1/send/xc8f41ea.234
09:35:38 856 MSG 2934573 Recipient: user01@umn.edu
09:35:38 856 MSG 2934573 Queuing message to daemon: /groupwise/dom/gwiadom1/wpgate/gwia1/send/sc8f41ea.234
09:35:38 864 DMN: MSG 2934573 Sending file: /groupwise/dom/gwiadom1/wpgate/gwia1/send/pc8f41ea.234
09:35:38 864 DMN: MSG 2934573 Attempting to connect to mhub-w.tc.umn.edu09:35:39 864 DMN: MSG 2934573 Connected to [134.84.119.108] (mhub-w.tc.umn.edu)
09:35:39 864 DMN: MSG 2934573 Connected to [134.84.119.108] (mhub-w.tc.umn.edu)
09:35:39 864 DMN: MSG 2934573 SMTP session ended: [134.84.119.108] (mhub-w.tc.umn.edu)

This has been ongoing for several months. The user it failed on in the first example could send the same message to the same recipient later on and the message goes through fine.

It looks like our mail server connects to the umn.edu mail server and then gets the Send Failure. And it's always the COMMAND UNRECOGNIZED: MAILXXXXXXXXXXXXXXXX's.

I thought it was some spam settings on the recipient side but am now not so sure. Anyone else seen this error or have any insight?

Kathy Tyler
North Memorial Medical Center