Here's a script I use to quickly recompile dovecot with vpopmail support on Debian 6.0. I'm using the backports repository to get the 2.1 version of dovecot.

Now I'm using the following script every time I update and I get a new version of the dovecot packages.

#!/bin/bash
 
BDIR=./dovecot.$(date +%Y-%m-%d_%H-%M-%S)
 
mkdir $BDIR
cd $BDIR 
 
sudo apt-get source dovecot-core
sudo apt-get build-dep dovecot-core
dpkg-source -x *.dsc 
 
cd $(find ./ -type d |grep dovecot|head -1) 
 
sed -r -e 's/with-sqlite \\/with-sqlite \\\n\t\t--with-vpopmail \\/' debian/rules > debian/rules.mod
cat  debian/rules.mod > debian/rules
 
DEB_BUILD_OPTIONS="--with-vpopmail" fakeroot debian/rules binary
 
find $BDIR -type f -name "*.deb"|grep -v 'dbg' |xargs dpkg -i
 
 

The last line also installs all the dovecot packages except for the debug one. You might want to change it if you don't want all.