If you are going to create a forwarded email address, do not create a pop account with the same name.
For example, if you are going to forward the email from email@example.com to firstname.lastname@example.org, do not create a pop account for email@example.com, just create the email forwarder. A pop mailbox does not have to exist for the mail to be forwarded.
If you create a pop account with the same name, and do not check the original pop account, this account gradually fill up with mail and over time may use up all of your available disk space. If you have any questions about this, please contact the helpdesk.