An automation script is deployed on a headless remote server to process system alerts. The script must periodically connect to a central mailbox, download new alert messages to process them, and immediately delete them from the mail server to prevent duplicate processing by other active instances of the script. To minimise protocol overhead on the low-resource server, the connection must be established over the standard, unencrypted port designated for this specific retrieval service.

Which protocol and default port combination must be configured for the script's retrieval mechanism?