Features:

• Plug-in to enhance composing and replying to messages in Apple's Mail.app
• Insert text snippets using shorthands; shorthand expansion is triggered by hot-key
• Insertion point position in a text snippet can be defined as part of the snippet
• Deletions of quoted text are marked with an ellipsis ("[...]")
• Define as many shorthands and text snippets as you want
• Supports left-to-right and right-to-left scripts
• Localized in English, German, Spanish, and French 

ComposeIT has been listed or rated at:

• Listed on Robin Benson's resource page at tikouka.net that focuses on plug-ins and tools for Apple Mail.
• Featured on Lifehacker in "How to Turn Mac Mail Into a Fantastic Email Client" (posted 2013-07-29) by Thorin Klosowski.

For the impatient: user's manual (new window)

Sytem Requirements:

• Mac OS X 10.7 (Lion), or better
• Using Apple's Mail.app as your email client

Installation:

• Download the installer below
• Launch it by double-clicking it

Revision History:

New in 2.0.4:

• Updated for compatibility with macOS 10.12.4 (Sierra) and Mail 10.3

New in 2.0.3:

• Updated for compatibility with macOS 10.12.2 (Sierra) and Mail 10.2

New in 2.0.2:

• Updated for compatibility with macOS 10.12.1 (Sierra) and Mail 10.1

New in 2.0.1:

• Updated for compatibility with macOS 10.12 (Sierra) and Mail 10.0

New in 2.0.0:

• New logo
• UI overhaul
• New installer

New in 1.5.1:

• Updated for compatibility with Mail 9.3 (OS X 10.11.4)

New in 1.5:

• Updated for compatibility with Mail 9 to 9.2 (OS X 10.11 to 10.11.3)
• under-the-hood updates

New in 1.4.7:

• Updated for compatibility with Mail 8.2 (2098) (OS X 10.10.3)

New in 1.4.6:

• Updated for compatibility with Mail 8.1 (1993) (OS X 10.10.1)

New in 1.4.5:

• Updated for compatibility with Mail 7.3 (1878.6) (OS X 10.9.4)

New in 1.4.4:

• Updated for compatibility with Mail 7.3 (OS X 10.9.3)
• Changed memory management from garbage collection (GC) to automatic reference counting (ARC)

New in 1.4.3:

• Updated for compatibility with Mail 7.2 (OS X 10.9.2)

New in 1.4.2:

• Updated for compatibility with Mail 7.1 (OS X 10.9.1)

New in 1.4.1:

• Fixed installer
• Installer now also signed with our developer ID

New in 1.4:

• Updated for compatibility with Mail 7.0 (OS X 10.9)
• Updated to latest version of ShortcutRecorder framework from GitHub (710c6be)

New in 1.3:

• Updated for compatibility with Mail 6.6 (OS X 10.8.5 update)

New in 1.2:

• Updated for compatibility with Mail 6.5 (OS X 10.8.4 update)

New in 1.1:

• Text snippets are searchable
• Mid-air collision warning prevents double shorthand assignment