I have used this application for some time with no problems at all.

After installing this update yesterday, I found my Mail app had stopped working. I could not quit (without Force Quitting), I could not open any emails in any folders, I could not delete any emails, I could not change any preferences, when opening Mail, most menu items were greyed out and the message viewer was not present. I could not download or send an emails.

After much discussion on the Apple Forums, I traced the problems to this application. Trashing it was not enough. I had to then find a bundle it created in the Mail Bundles Folder, remove that and restart Mail. Now Mail is working perfectly as it was before this update.