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I have a user that cannot authenticate. What I am getting is:

did not issue MAIL/EXPN/VRFY/ETRN during connection to MTA

I have SASL installed for plaintext passwords. Can someone please point me in the right direction? What am I missing?

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1. The error message does not have anything to do with authentication. 2. Neither does TLS (if you are using SASL for auth). – grawity Mar 4 '11 at 6:21

The error message means that the client opens up a connection to port 25 on your server, but does not issue any other commands. I will make a wild guess here and will suspect that this is a TCP window scaling problem. If the client is a Windows Vista / 7 machine try something like:

netsh interface tcp set global autotuninglevel=disabled


netsh interface tcp set global autotuninglevel=restricted

from a command prompt that you have started as an administrator. If your server is a linux machine you can try adding these at the bootom of your /etc/sysctl.conf:

 net.ipv4.tcp_rmem = 4096 87380 174760
 net.ipv4.tcp_wmem = 4096 16384 131072
 net.ipv4.tcp_window_scaling = 0

Run "sysctl -p" as root for the changes to take effect. Depending the case you may need both. However this is a workaround and not a solution to the problem, and like I said a wild guess since I've seen such behaviour coupled with the error message that you describe too many times.

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My monitoring system tries to make a TCP connection to my mail server's port 25 and see a sendmail banner; if it does, it promptly disconnects, which produces exactly this log message. So yes, there are many reasons this message might appear in your logs. – MadHatter Aug 13 '15 at 7:08

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