The next best thing to Mail.app is a copy of Thunderbird skinned to look like Mail. At least, that was clearly the case until GyazMail got IMAP support.
Another Apple Mail skin has appeared for Thunderbird, bringing the total to three.
This one, called “Apple Mail”, offers the Tiger Mail look.
The developer says it “makes your TB look and feel like the native Apple Mail software, that comes along wiht your shiny and flashy new Mac.”
Things start to fall apart a bit in the Compose window though:
The “Tiger Mail” theme offers Thunderbird users the same look.
CrossOver provides a Panther Mail look.
Take a look at both of them in an earlier Hawk Wings post and/or go grab Apple Mail 
from the Thunderbird Add-ons site.
FWIW, none of these themes work well, if at all, with Thunderbird 2.x. A shame too…
Thunderbird 2.0 b2 sports an updated pinstripe theme that I like quite a bit. Still has the old T-bird icons but a bit more Mac-ness.
Thunderbird 2.0 b2 sports an updated pinstripe them that gives it a bit more mac-iness.
Seeing as Thunderbird 2 has not been released, the majority of users are still using 1.5 so that’s what the theme is designed for. And it looks fantastic. :)
Gee, the compose window looks cluttered.
Can’t make a silk purse out of a sow’s ear?
So, Tim, you rank Apple Mail number 1, Gyazmail number 2, and Thunderbird in various clothes number 3…. ? :-)
Steve
That’s about it. As far as Desktop clients go. Even I wasn’t such a bigot, I might rate Entourage higher. In any case, the gap between 1 and 2 is pretty big!