Add additional recipient

`Alt` + `Arrow Down`

All hotkeys for Thunderbird (MacOS)

Navigate Messages Toggle Message Pane	`F8`
Navigate Messages Switch focus between Folders Pane and Message List Pane	`F6` / `Tab` / `Shift` + `Tab`
Navigate Messages Go one message down / one message up	`Arrow Down` / `Arrow Up`
Navigate Messages Go to first message / go to last message	`Home` / `End`
Navigate Messages Go to next / go to previous message	`F` / `B`
Navigate Messages Go to next / go to previous unread Message	`N` / `P`
Navigate Messages Go to previously viewed / go to next viewed Message	`[` / `]`
Navigate Messages Open message (in new window or tab)	`Command` + `O` / `Enter`
Navigate Messages Close window or tab	`Command` + `W`
Navigate Messages Redo close window or tab	`Command` + `T`
Navigate Messages Select all messages	`Command` + `A`
Navigate Messages Select all messages in Thread	`Command` + `Shift` + `A`
Navigate Messages Expand / collapse collapsed Thread	`Arrow Right` / `Arrow Left`
Navigate Messages Expand all Threads / collapse all Threads	`*` / `\`
Compose and Edit Message New Message	`Command` + `N`
Compose and Edit Message Reply to Message (sender only)	`Command` + `R`
Compose and Edit Message Reply to all in Message	`Command` + `Shift` + `R`
Compose and Edit Message Reply to list	`Command` + `Shift` + `L`
Compose and Edit Message Forward Message	`Command` + `L`
Compose and Edit Message Edit Message as new	`Command` + `E`
Compose and Edit Message Send Message now	`Command` + `Enter`
Compose and Edit Message Send Message later	`Command` + `Shift` + `Enter`
Compose and Edit Message Add additional recipient	`Alt` + `Arrow Down`
Compose and Edit Message Increase / decrease text size of selection	`Command` + `[` + `]` / `-`
Compose and Edit Message Copy / Cut / Paste	`Command` + `C` / `Command` + `X` / `Command` + `V`
Compose and Edit Message Paste as quotation	`Command` + `Shift` + `O`
Compose and Edit Message Paste without formatting	`Command` + `Shift` + `V`
Compose and Edit Message Select all text in a message	`Command` + `A`
Compose and Edit Message Save draft	`Command` + `S`
Compose and Edit Message Delete current word	`Command` + `Delete`
Compose and Edit Message Delete previous word	`Command` + `Backspace`
Mark, Delete and Move Message Mark Message as read / unread	`M`
Mark, Delete and Move Message Mark Message Thread as Read	`R`
Mark, Delete and Move Message Mark all Messages als Read	`Shift` + `C`
Mark, Delete and Move Message Mark as Read by date	`C`
Mark, Delete and Move Message Mark as Junk / mark as not junk	`J` / `Shift` + `J`
Mark, Delete and Move Message Add / remove Star	`S`
Mark, Delete and Move Message Archive Message	`A`
Mark, Delete and Move Message Move to previous folder	`Command` + `Alt` + `M`
Mark, Delete and Move Message Delete message	`Delete`
Mark, Delete and Move Message Delete with bypassing trash	`Shift` + `Delete`
Mark, Delete and Move Message Ignore or Unignore Thread	`K`
Mark, Delete and Move Message Ignore or Unignore Subthread	`Shift` + `K`
Mark, Delete and Move Message Watch Thread	`W`
Mark, Delete and Move Message Add / remove Tag 1 ... 9	`1` ... `9`
Mark, Delete and Move Message Remove all Tags from Message	`0` (zero)
Find Messages Find Messages with Quick Filter	`Command` + `F`
Find Messages Find all Messages in Folder	`Command` + `Shift` + `F`
Find Messages Find text in current Message	`Command` + `f` and `command` + `f` again
Find Messages Find text again next in Current Message	`Command` + `G` / `F3`
Find Messages Find text again previous in Current Message	`Command` + `Shift` + `G` / `Shift` + `F3`
Find Messages Move to Search Bar	`Command` + `K`
Retrieve Messages Send and retrieve all messages	`Command` + `T` / `F5`
Retrieve Messages Retrieve new messages for current account	`F5`
Retrieve Messages Retrieve new messages for all accounts	`Command` + `Shift` + `T`
Retrieve Messages Stop	`Esc`
Other Shortcuts View Message Source	`Command` + `U`
Other Shortcuts Save Message as File	`Command` + `S`
Other Shortcuts Print	`Command` + `P`
Other Shortcuts Undo	`Command` + `Z`
Other Shortcuts Redo	`Command` + `Y`
Other Shortcuts Caret browsing (select text with keyboard)	`F7`
Other Shortcuts Help	`Command` + `?`
Other Shortcuts Open 'Saved Files' Window	`Command` + `J`
Other Shortcuts Increase / decrease text size (zoom)	`Command` + `[` + `]` / `-`
Other Shortcuts Restore Text Size (reset zoom)	`Command` + 0 (zero)Command + 0 (zero)Ctrl+ `0`
Other Shortcuts Open Address Book	`Command` + `Shift` + `B`
Other Shortcuts Exit	`Command` + `Q`