Jonas from the maurus.net weblog is writing down some qmail recipies. The first entry is about “Forwarding mail and changing the envelope sender”.
I guess for everyone who is interested in qmail and working with it, there will be some helpful insights.

since the new gcc version is out, djb software has its problems with compiling. also netqmail has problems.
something with errno … bla…bla…bla…

there is a simple fix for that.
just go to the sourcecode and find the file conf-cc.
edit it and add the following code :
cc -O2 -include /usr/include/errno.h

now it should work.

after looking around, i found this entry in life with qmail. after changing all things descriped there, my qmail is running and running and breaking records. 🙂

in addition to that, you should look here at tcpserver config

i use qmail in combination with vpopmail from inter7 on my servers.

the most start scripts for qmail use tcpserver and tcpserver uses recursive dns for every request.
so if there is a lot of traffic or spam or whatever, tcpserver sometime takes to long to resolv these ip addresses and no more connections are able to be opened in that time.
the resultion is to set the params like this:

tcpserver -H

the -H means don’t resolve the ip.