Type the addresses into the field on the invitation dialog. The Invite button becomes active as soon as you start typing — you do not have to press anything first.

Separate addresses with a comma, a semicolon or a space (a new line works too). Each finished address turns into a chip. Enter does the same thing, but it is optional now: whatever is still in the field when you press Invite is sent along with the chips.

Backspace on an empty field removes the last chip.

If one of the addresses is not a valid address, nothing is sent and the platform names the address that is wrong. Correct it and press Invite again.

An address you have already invited is skipped. The dialog reports success, but no second letter goes out to someone whose invitation is still pending or already accepted.