To delete a custom email address, you must first delete the emails associated with it. This is because the keys paired with the email address are also deleted in the process, and you will no longer be able to read your emails (since they cannot be decrypted). If there are emails that have not been deleted, you will receive an error message:
1. The easiest way to locate all your emails for a specific email address is through the advanced search option located at the top of your inbox. Click on the Arrow button beside the search bar.
2. Under Address, select the email address you want to delete from the dropdown menu and click Search.
3. The search results will only include the emails you have received at this address. Select all of them by checking the box at the top and delete them by clicking on the Trash icon.
4. Now click on Trash in the left sidebar. Select all emails by checking the box at the top and permanently delete them by clicking on the X button.
5. You should now be able to delete your custom email address. Click on Settings and Go to Settings at the top right of your inbox.
6. Select Identity and addresses in the left sidebar. Under Edit user, select the email address you want to delete and click on Delete. Your custom email address is now deleted.
Note: Email addresses with the default domains protonmail.com, protonmail.ch, and pm.me can only be disabled, not deleted.