Section labeled "Don't forget to remove" is actually impossible to remove in GMail

[obadz]

Prerequisites

• [x] I have searched open and closed issues to make sure that the bug has not yet been reported.

Bug report

Describe the bug

When a mailbox sends a reply to an alias associated with more than one mailbox, the other mailboxes get a copy of the reply (which is great). There's a header informing the other mailboxes about which mailbox sent the reply (non-essential imho).

This header instructs the user to not forget to remove it, see code: https://github.com/simple-login/app/blob/fa88c935d3b9cb381baff76a0138596853734272/email_handler.py#L1326-L1330

However, the HTML inserted in the reply is impossible to completely remove at least in the GMail web app: https://github.com/simple-login/app/blob/fa88c935d3b9cb381baff76a0138596853734272/app/email_utils.py#L983-L995

The text can be deleted, but the dotted line always remain because it is part of the table that contains the entire message.

Expected behavior

I'd expect an info message that can be removed easily in all commonly used E-mail platforms or better yet, no info message at all so that replying would be more fluid. The name of the mailbox can be added to an X- header if it's essential for the other mailboxes to have this information.

Screenshots

Replying to an E-mail with the info requires removing this line:

The text can be removed but the dotted line persists:

Environment (If applicable):

• OS: Linux
• Browser: Firefox
• Version 139.0.1