MailRecent (Mail Plugin for Mac OS X) Adds "Copy to Recent," "Move to Recent," and "Go to Recent" menu items to Apple's Mail application. These menu items contain dynamically-updated lists of recently used mailboxes. The number of mailboxes kept in the list is determined by the "Number of Recent Items" setting for Documents in the Appearance panel of the OS X System Preferences.


Author's Note: As of 2.0, I am providing the plugin only. I cannot provide an installer, and you must perform a manual installation as described below.
You might need to provide Full Disk Access for the Terminal application to successfully use the following commands. You should remove this elevated Terminal permission after you have issued the commands.

Also, as of macOS 10.4.2/Mojave, Apple has incorporated a new Mail plugin management scheme. After you install any plugin (including mine) you must enable them from within Mail per steps 5–9 below.

1. Quit the Mail application.
2. Download (see above), expand, and mount the MailRecent disk image.
3. Drag MailRecent.mailbundle to ~/Library/Mail/Bundles/ ("~"means a user's home directory). You might need to create the Bundles folder if it does not already exist.
4. If you have never used another Mail bundle, you will need to run two special commands in the Terminal application (omit the % prompt).
% defaults write ~/Library/Containers/com.apple.mail/Data/Library/Preferences/com.apple.mail.plist EnableBundles -bool true
% defaults write ~/Library/Containers/com.apple.mail/Data/Library/Preferences/com.apple.mail.plist BundleCompatibilityVersion 4
5. Launch the Mail application again.
6. Select “Preferences…” from the Mail menu.
7. In the General tab click the "Manage Plug-Ins…” button near the bottom left.
8. Select (check the box for) each plugin that you want to use.
9. Click the "Apply and Restart Mail” button.

After Mail relaunches the plugin(s) should be available, assuming all else is correct/well.


Requirements:
OS X 10.14+
Intel

Also available are:
Version 1.7 for OS X 10.13
Version 1.6.4 for OS X 10.12.4
Version 1.6 for OS X 10.11
Version 1.5.2 for OS X 10.10
Version 1.4.5 for OS X 10.9
Version 1.3.9 for OS X 10.8
Version 1.3.6 for OS X 10.7
Version 1.2.5 for OS X 10.6
Version 1.1 for OS X 10.5
Version 1.0.4 for OS X 10.4