My installation is just about working. I use fetchmail to retrieve the mail from my two POP3 accounts and have qmail running and pine configured to use the fake sendmail binary that came with qmail.

If I receive mail, everything's fine. But if I want to send mail I need to rewrite the from address from username@somewhere.domain.com to otheruser@domain.com.
If I add this to the environment:

MAILHOST=domain.com
MAILUSER=otheruser
QMAILINJECT=f

Then when qmail-inject is called from pine (through the fake sendmail) it rewrites the header correctly. The big problem with this is that the header is also rewritten if fetchmail calls qmail-inject, so every incoming mail looks like it's coming from otheruser@domain.com.

How can I fix this?

easiest way is to just set the header in pine in the customized-hdrs sectino in the setup. its not a particuarly nice thing to do, but then no worse than needing to lie about your domain name in the first place...

I've tried what you said, but it's not quite working.

Here's some data:
- The user name at the local computer of the user starting pine is 'username'
- The host that's running qmail and pine is 'hostname.somewhere.com'
- The user name at the mail server is 'othername'
- The domain for which the mail server is handling mail is 'somewhere.com'
- The hostname of the mail server is 'realname.somewhereelse.com'

Like I said I would like to be able to send mail with 'othername@somewhere.com' in the From line. But now I have 'username@somewhere.com' in there.

From /etc/pine.conf:
sendmail-path=/usr/lib/sendmail -oem -oi -t
(which is the sendmail wrapper provided by qmail)

/home/username/.qmail:
./Maildir/

/home/username/.fetchmailrc:
poll realname.somewhereelse.com
protocol POP3 username 'othername' password 'somepassword' is username here
forcecr fetchall
mda "/var/qmail/bin/qmail-inject username"

From /home/username/.pinerc:
user-domain=somewhere.com
customized-hdrs=From: Myname <othername@somewhere.com>

I have also tried using
sendmail-path=/usr/lib/sendmail -oem -oi -t -fothername@somewhere.com
and
sendmail-path=/usr/lib/sendmail -oem -oi -t -fothername
in /etc/pine.conf, but that didn't work either.

In /var/log/qmail.log I can see:
info msg 292298: bytes 346 from <othername@somewhere.com> qp 12600 uid 501
starting delivery 23: msg 292298 to remote someguy@computer.net
status: local 0/20 remote 1/90
delivery 23: success: xxx.xxx.xxx.xxx_accepted_message./Remote_host_said:_250_2.0.0_g08M8ROf072068_Message_accepted_for_delivery/
status: local 0/20 remote 0/90
end msg 292298

But still that person saw the mail came from username@somewhere.com.

Help, pls! =(