Underline

`Command` + `U`

All hotkeys for Apple Mail (MacOS)

Editing Shortcuts Archive an email message	`Command` + `Down Arrow`
Editing Shortcuts Bold	`Command` + `B`
Editing Shortcuts Compose a new email message	`Option` + `Shift` + `N`
Editing Shortcuts Delete a selected message or folder	`Delete`
Editing Shortcuts Flag or unflag email	`Shift` + `Command` + `L`
Editing Shortcuts Indent items in a list	`Command` + `]`
Editing Shortcuts Italic	`Command` + `I`
Editing Shortcuts Make font size bigger	`Command` + `=`
Editing Shortcuts Make font size smaller	`Command` + `-`
Editing Shortcuts Mark email as Junk or Not Junk	`Shift` + `Command` + `J`
Editing Shortcuts Mark email as Read or Unread	`Shift` + `Command` + `U`
Editing Shortcuts Open the selected message in a new window	`Return`
Editing Shortcuts Outdent items in a list	`Command` + `[`
Editing Shortcuts Print	`Command` + `P`
Editing Shortcuts Redo changes to an email message	`Shift` + `Command` + `Z`
Editing Shortcuts Reply to sender	`Shift` + `Command` + `R`
Editing Shortcuts Save as a draft	`Command` + `S`
Editing Shortcuts Scroll through the selected messages	`Spacebar`
Editing Shortcuts Select all email messages	`Command` + `A`
Editing Shortcuts Send email message	`Shift` + `Command` + `D`
Editing Shortcuts Toggle between Reply and Reply All	`Shift` + `Command` + `R`
Editing Shortcuts Underline	`Command` + `U`
Editing Shortcuts Undo changes to an email message	`Command` + `Z`
Sending Messeges New Message	`Command` + `N`
Sending Messeges Send Message	`Command` + `Shift` + `D`
Sending Messeges Save Draft	`Command` + `S`
Sending Messeges Forward Message	`Command` + `Shift` + `F`
Sending Messeges Attach File	`Command` + `Shift` + `A`
Sending Messeges Show/Hide bcc field	`Command` + `Option` + `B`
Receive Message Flag Message	`Command` + `Shift` + `L`
Receive Message Reply to Message	`Command` + `R`
Receive Message Reply to All	`Command` + `Shift` + `R`
Receive Message Move message to same box you just did	`Command` + `Option` + `T`
Receive Message Mark as read/unread	`Command` + `Shift` + `U`
Receive Message Mark as junk mail	`Command` + `Shift` + `J`
Receive Message View raw message content	`Command` + `Option` + `U`
Receive Message
Formatting Messages Show fonts panel	`Command` + `T`
Formatting Messages Show colors panel	`Command` + `Shift` + `C`
Formatting Messages Align Right	`Command` + `Shift` + `]`
Formatting Messages Align Left	`Command` + `Shift` + `[`
Formatting Messages Align Center	`Command` + `Shift` + `\|`
Formatting Messages Copy Style	`Command` + `Option` + `C`
Formatting Messages Paste Style	`Command` + `Option` + `V`
Formatting Messages Check Spelling	`Command` + `Shift` + `;`
General Shortcuts Get New Mail	`Command` + `Shift` + `N`
General Shortcuts Open message viewer	`Command` + `O`
General Shortcuts Add sender to address book	`Command` + `Shift` + `Y`
General Shortcuts Use selected text in search	`Command` + `E`
General Shortcuts Go to Inbox	`Command` + `1`
General Shortcuts Jump to search field	`Command` + `Option` + `F`
General Shortcuts Go to other items in favourites	`Command` + `2..9`
General Shortcuts Apply Rule to selected message	`Command` + `Option` + `L`