SMTP submission error

Is this an Exchange SMTP server (based on what I found here)?

Try opening the Activity Viewer (⌥⌘0) and then send a message (maybe after relaunching MailMate to clear all state). Then locate the SMTP connection used for the attempt to send and select it to see the log in the lower part of the window. Maybe that can provide a hint. You are welcome to send it to me.

It is indeed an exchange server (2011). The trace from the log is

S: 220 mail.dlpe.gatech.edu<http://mail.dlpe.gatech.edu> Microsoft ESMTP MAIL Service ready at Wed, 11 Dec 2013 08:47:05 -0500
C: EHLO [192.168.1.110]
S: 250-mail.dlpe.gatech.edu<http://250-mail.dlpe.gatech.edu> Hello [10.41.1.181]
S: 250-SIZE 104857600
S: 250-PIPELINING
S: 250-DSN
S: 250-ENHANCEDSTATUSCODES
S: 250-STARTTLS
S: 250-AUTH GSSAPI NTLM
S: 250-8BITMIME
S: 250-BINARYMIME
S: 250 CHUNKING
C: STARTTLS
S: 220 2.0.0 SMTP server ready
Initiating SSL/TLS...
Setup of SSL/TLS connection complete.
C: EHLO [192.168.1.110]
S: 250-mail.dlpe.gatech.edu<http://250-mail.dlpe.gatech.edu> Hello [10.41.1.181]
S: 250-SIZE 104857600
S: 250-PIPELINING
S: 250-DSN
S: 250-ENHANCEDSTATUSCODES
S: 250-AUTH GSSAPI NTLM LOGIN
S: 250-8BITMIME
S: 250-BINARYMIME
S: 250 CHUNKING
C: AUTH LOGIN
S: 334 VXNlcm5hbWU6
C: ••••••••••
S: 334 UGFzc3dvcmQ6
C: ••••••••••
S: 235 2.7.0 Authentication successful
C: RSET
S: 250 2.0.0 Resetting
C: MAIL FROM:<hic@cc.gatech.edu<mailto:hic@cc.gatech.edu>> SIZE=2095
S: 452 4.3.1 Insufficient system resources
Error: Unexpected return code 452 (expected 250):
“4.3.1 Insufficient system resources”.
C: QUIT

Surprised that I am not getting any problems with other mailers. I have asked our helpdesk to check the log on server side. Best

The MAIL FROM value looks strange. Where does the mailto: stuff come from? Maybe check your IMAP account settings.

Other than that, it looks fine, but note that the error message has changed. It now seems to indicate that the server does not have enough space for the message...

I have been playing around here. Is another log dump

Clearing connection to ccmail.cc.gatech.edu
Trying to connect to ccmail.cc.gatech.edu on port 587
Successful connection.
S: 220 mail.dlpe.gatech.edu Microsoft ESMTP MAIL Service ready at Wed, 11 Dec 2013 09:27:24 -0500
C: EHLO [192.168.1.110]
S: 250-mail.dlpe.gatech.edu Hello [10.41.1.181]
S: 250-SIZE 104857600
S: 250-PIPELINING
S: 250-DSN
S: 250-ENHANCEDSTATUSCODES
S: 250-STARTTLS
S: 250-AUTH GSSAPI NTLM
S: 250-8BITMIME
S: 250-BINARYMIME
S: 250 CHUNKING
C: STARTTLS
S: 220 2.0.0 SMTP server ready
Initiating SSL/TLS...
Setup of SSL/TLS connection complete.
C: EHLO [192.168.1.110]
S: 250-mail.dlpe.gatech.edu Hello [10.41.1.181]
S: 250-SIZE 104857600
S: 250-PIPELINING
S: 250-DSN
S: 250-ENHANCEDSTATUSCODES
S: 250-AUTH GSSAPI NTLM LOGIN
S: 250-8BITMIME
S: 250-BINARYMIME
S: 250 CHUNKING
C: AUTH LOGIN
S: 334 VXNlcm5hbWU6
C: ••••••••••
S: 334 UGFzc3dvcmQ6
C: ••••••••••
S: 235 2.7.0 Authentication successful
C: RSET
S: 250 2.0.0 Resetting
C: MAIL FROM:<hic@cc.gatech.edu> SIZE=2097
S: 452 4.3.1 Insufficient system resources
Error: Unexpected return code 452 (expected 250):
“4.3.1 Insufficient system resources”.
C: QUIT

It does appear to be a "space"/resource issue server side, but I do not get any errors when sending the same message from the OSX Mail client.

Maybe you don't use the IMAP access with Apple Mail and that makes a difference?

True. I am using the Mail exchange link, but I have used airmail with the imap and still not getting the error message. My preference is mail clients i) mailmate, ii) airmail and iii) osx mail. Not sure what has changed. Could be server side or client slide. I am using the latest mailmate - Version 1.7.1 (3836) - with version 2 features enabled.

One possible difference. The server claims to support the SIZE extension. MailMate supports that and tells the server the size of the message to be uploaded. Maybe this triggers a bug in Exchange that the other email clients do not trigger.

Other than that I cannot see any potential problems.

Not sure. I have asked our enterprise people to send me a copy of the relevant part of the log, so that I can see what is happening server side. Stay tuned. Thank you for your support.