Disabling Non-Webmail access blocks the IMAP, POP3, and SMTP connections to the mailbox. As a result, scripts and mail clients (like MS Outlook, Thunderbird, and Apple Mail) using the IMAP/POP3/SMTP protocols will no longer be able to connect to the mailbox. Combining this with two-factor authentication greatly enhances the mailbox security; however, it also means that the mailbox can only be accessed via Webmail Classic and Roundcube. 

Non-Webmail access can be controlled per mailbox via the Mail Manager in the Control Panel:

  1. Log in to the Control Panel, and go to the Mail Manager section.
  2. Click on the Gear button next to the mailbox > 2FA & Non-Webmail Access (IMAP/POP3/SMTP).
  3. Click on the toggle next to Non-Webmail access (IMAP/POP3/SMTP).

When the toggle is off, Non-Webmail access is blocked, so the mailbox is only accessible via Webmail Classic and Roundcube.

You can also disable and enable Non-Webmail access through Webmail Classic and Roundcube. Detailed instructions on how to do so are available in the Non-Webmail Access Control article.