From Bugzilla Helper:
User-Agent: Mozilla/4.76 [en] (X11; U; Linux 2.2.19-6.2.1 i686)

Description of problem:
In a setup where my box is a relay only MX for 'otherdomain.com'
mail is flowing fine from everywhere->myhost->otherdomain.com but does not
go in the other direction: otherdomain.com->myhost->rest-of-the-world.

I had the following lines in /var/log/maillog 

 May 28 11:19:41 myhost sendmail[12697]: f4S8Jdk12697: timeout waiting
for input from mail.otherdomain.com during message collect
 May 28 11:19:41 myhost sendmail[12697]: f4S8Jdk12697:
from=<X.Y>, size=0, class=0, nrcpts=1,
msgid=<200105280819.f4S8Jdk12697.com>, proto=ESMTP,
daemon=Daemon0, relay=mail.otherdomain.com [1.2.3.4]
 May 28 11:19:41 myhost sendmail[12697]: f4S8Jdk12697: to=<xy>,
delay=01:00:02, pri=30000, relay=yahoo.it., stat=timeout waiting for
input during message collect

You may notice two strange things in the log:
1) size is zero: this is "correct": I traced messages exchanged in the
protocol and after EHLO ...... myhost there is the 
  <<< DATA  
  >>> 354 Enter mail, end with "." on a line by itself
dialog that exits with timeout (and so size=0).
2) in the to=<...> line we have relay=yahoo.it. and not something like
relay=host.yahoo.it. 

This is a visible simptom: in the sending phase relay= is always a
domain, not an host. I don't understand why!

How reproducible:
Always

Steps to Reproduce:
1. have two hosts: A and B, A cannot reach internet, B is his mail relay
2. describe this setup in DNS: A is higher precedence MX, B the other one
3. B also is the mail forwarder for A
4. send a mail from A to yourfriend

Actual Results:  A tries to send the mail to B but in the collect phase B
has a timeout and does not get any data.

Expected Results:  mail from A delivered to yourfriend

Additional info:

Michael Abadjiev suggested to me that sendmail-8.11.2 is broken and to grab
sources from sendmail-8.11.0 (RedHat 7.0); done, rebuild (on RH 7.1) and
all went fine.