[Wlug] Possible sendmail attack?

[Dick Goodman]

I have four servers on 3 different DSL lines running RedHat 7.3 with 
sendmail 8.11.6

I was on vacation at the time, but mid-day (13:00) on January 9th all of 
them started behaving wierdly.

Instead of the  occassional email, perhaps 95% of all incoming emails now 
show in the log as follows:

Jan  9 09:41:17 bach sendmail[25179]: NOQUEUE: mail5.schaeffer.com 
[24.106.95.27] did not issue MAIL/EXPN/VRFY/ETRN during connection to MTA
Jan 11 00:02:12 bach sendmail[14018]: NOQUEUE: h11009.upc-h.chello.nl 
[62.194.11.9] did not issue MAIL/EXPN/VRFY/ETRN during connection to MTA
Jan 11 00:10:44 bach sendmail[14127]: NOQUEUE: 
bay0-omc2-s35.bay0.hotmail.com [65.54.246.171] did not issue 
MAIL/EXPN/VRFY/ETRN during connection to MTA
Jan 11 00:13:23 bach sendmail[14148]: NOQUEUE: root at localhost did not issue 
MAIL/EXPN/VRFY/ETRN during connection to MTA
Jan 11 00:13:50 bach sendmail[14151]: NOQUEUE: 
84.95.106.53.cable.012.net.il [84.95.106.53] did notissue 
MAIL/EXPN/VRFY/ETRN during connection to MTA

The first one is legitimate mail, the others appear to be spam

Much of the 50K pieces/month of spam I get are being trapped at the server 
in this manner before even getting to my spam filters (a good thing), but 
while some legitimate email is getting through, some is being rejected with 
this kind of message.

Does anyone (a) have any idea what's happening here (b) have any idea how 
to fix it.

Need more info? Just ask.
Dick