In ProtonMail, labels and folders are two tools to help organize your Mailbox. ProtonMail has seven default folders into which your emails can be sorted: All Mail, Inbox, Drafts, Sent, Starred, Archive, Spam, and Trash. Users can also create custom folders. Labels, on the other hand, are like tags that you can add to your emails.
The email clients supported by the Bridge interpret ProtonMail labels as folders. So when you configure your ProtonMail account with your email client, your existing labels will appear as folders within the Labels folder.
How to apply labels in the Bridge
If you want to “label” a ProtonMail message in your email client, there are two ways to do so:
If you want to label the message without removing it from its current location, right click on the message, select Copy To and choose the label folder you want.
In the email clients we support, labels are known as tags. Unfortunately, the Bridge does not support tags. Therefore, if you tag messages in your email client, these will not be integrated with your Mailbox in ProtonMail.