Can't send emails through sendmail, error occured

Question

I have sendmail MTA and I use pear:Mail class to send mails through remote sendmail server. Everything was fine till yesterday. Probably nothing changes was made in configs.

At maillog I can see:

May  6 12:58:55 xxx sendmail[25903]: STARTTLS=server, relay=hostxxxx.static.xx.xx.pl [85.x.x.x], version=TLSv1/SSLv3, verify=NO, cipher=DHE-RSA-AES256-SHA, bits=256/256
May  6 12:58:56 xxx sendmail[25903]: o46AwtqE025903: hostxxxx.static.xx.xx.pl [85.x.x.x] did not issue MAIL/EXPN/VRFY/ETRN during connection to MTA2

and in /var/log/messages:

May  6 13:00:17 lilia sendmail[27193]: realm changed: authentication aborted

I use ldap to authenticate users but I used the same script to check mailing on another server and it works there good, only this server behave weird. Packets are delivered to sendmail server I can see it in tcpdump, but there is smaller packets than on other server which sends emails.

Could you tell me how can I check what is wrong with that?

Answer 1

Was there a kernel upgrade? Try to disable TCP window scaling and see if the problem persists. Add in your /etc/sysctl.conf

net.ipv4.tcp_window_scaling = 0

and run sysctl -p as root next. If disabling window scaling works, keep in mind that it is a workaround and not a solution to your problem.