Control-Command-W
Make the text bigger
Command-Plus Sign (+)
Make the text smaller
Command-Minus Sign (–)
Insert a line break (in a message)
Option-Return
Copy the selected text
Command-C
Paste copied text
Command-V
Open the Spelling and Grammar window
Shift-Command-Colon (:)
Check the text field for spelling and grammar issues
Command-Semicolon (;)
Select the next conversation
Control-Tab
Select the previous conversation
Control-Shift-Tab
Send an email to a selected person in the conversation
Option-Command-E
Show video effects (while in a video call in Messages)
Shift-Command-E
Close all conversations
Option-Shift-Command-W