How to mark all messages in a Gmail mailbox as read

Gmail allows you to mark emails as read only on one page worth at a time. Infuriating if you have a backlog of unread messages in your mailbox - as I do.

How to mark ALL messages in the mailbox as read at once?

Easy:

Select All or Unread messages on the page, at which point you will see a little message at the top of the list: "All XX conversations on this page are selected. Select all YYY conversations in "MailBox"

Click on this "link": Select all YYY conversations in "MailBox"

At that point you will see the message: All YYY conversations in "MailBox" are selected. Clear selection

Now that all messages are selected, click on More/Mark As Read.

Confirm the bulk action...

Done.