Just for fun, I built Mozilla Thunderbird from the latest sources using Microsoft Visual C++ .NET 2003.

Optimized for Pentium 4, Pentium M, Celeron 1.7GHz+ and Athlon64 with SSE2. I stripped out most of the stuff I don't need, and added compiler optimizations /G7 (optimize for processors listed above) and /Oxs (full optimization, optimize for size).

Download it: thunderbird-win32-20040201-Oxs-G7-SSE2.zip

Here's my .mozconfig:

export MOZ_THUNDERBIRD=1
mk_add_options MOZ_THUNDERBIRD=1

ac_add_options --disable-accessibility
ac_add_options --disable-activex
ac_add_options --disable-activex-scripting
ac_add_options --disable-auto-deps
ac_add_options --disable-crypto
ac_add_options --disable-debug
ac_add_options --disable-freetype2
ac_add_options --disable-installer
ac_add_options --disable-jsd
ac_add_options --disable-ldap
ac_add_options --disable-mathml
ac_add_options --disable-necko-disk-cache
ac_add_options --disable-oji
ac_add_options --disable-profilesharing
ac_add_options --disable-tests
ac_add_options --disable-xprint

ac_add_options --enable-extensions=wallet,xmlextras
ac_add_options -enable-image-decoders=bmp,jpeg,gif,icon,png
ac_add_options --enable-necko-protocols=http,file,jar,viewsource,res,data
ac_add_options --enable-optimize='-Oxs -G7 -arch:SSE2'
ac_add_options --enable-strip