3 in 1:
1st)
The splash screen of the app shows a link to portableapps.com/go/thunderbirdportable which like is dead.
2nd)
You have Sunbird 1.0 and Lightning 1.0 on your site. Mozilla recommends instead of both the actual Lightning extension for Thunderbird (current version 1.9) which is of course totally portable and compatible with your version of Thunderbird.
3rd)
There is a version of Portable GPG in an obscured place of your site. It was a "one-off" shot, or will it be regularly updated, will the user be able to update it from the PortableApps platform? I know that's a tricky one.
Keep up the god work!
1) The link has been fixed
2) Some people like to use Sunbird still. We note that it is no longer developed
3) We update the GPG add-on for Thunderbird regularly. It is not updated by the PortableApps.com Platform. Only apps and CommonFiles add-ons (like Java) are automatically updated. App add-ons are not.
Sometimes, the impossible can become possible, if you're awesome!
1) It still looks the same from here.
2) About Lightning it's still a little confusing that your link says 1.0, how ever it points to 1.9 on Mozilla's home page. No big deal.
All in all: thanks for your work John!