You will be asked to enter your Bridge password twice (for IMAP and SMTP). Note: The password you must use is automatically generated from the bridge. Do not use your Login or Mailbox password.
The password generated by the Bridge app can be found by by clicking on Mailbox configuration under your account username.
You may see a security warning. If you do, click Yes.
After adding your account, you need to navigate to File Account Settings Account Settings
Select your ProtonMail account and click the Change ... button.
In the Sent Items category, select Do not save copies of sent items and in the Deleted Items category, select Purge items when switching folders while online. Click OK.
Note: In separate addresses mode every IMAP account that you set up with the Bridge is address-specific, and will only be able to send/receive emails from the address it is set up with. You can add any number of addresses to Outlook but wait for one address to download before adding another.
Note: In combined address mode Outlook has no way to add the other addresses to send with.