Mail aging is the process in which e-mails will be removed from the server automatically, upon successful log out of a pop3 session. This deletion will only occur if the messages are older then a specified amount of days.
Aging will only work with POP3
To clarify, I think there are (at least) 2 different features that we are referring to as "Aging".
#1. The feature labelled "Aging" in cPanel > Mail > Manage/Add/Remove accounts. As far as I can tell, this is feature on the server that removes old emails from inboxes that have been marked as READ by an IMAP client.
#2. A feature of most POP3 clients, where the messages left on the server for a certain number of days.
I was referring to #1, the cPanel feature, when I started this topic.
I understand that it will only work for IMAP users. Because this server enforced "Aging" only removes messages that have been marked as read by IMAP clients. POP3 does not change the READ-status of messages as required.