The menu Email Protection > POP3 lets you configure the POP3 proxy for incoming emails. The Post Office Protocol 3 (POP3) is an application-layer Internet standard protocol that allows the retrieval of emails from a remote mail server. The POP3 proxy works transparently, meaning that all POP3 requests coming from the internal network on port 110 (and 995 if scanning of TLS encrypted traffic is enabled) are intercepted and redirected through the proxy invisible to the client. The advantage of this mode is that no additional administration or client-side configuration is necessary.
Note – It might be necessary to increase the server timeout settings in the email clients' configuration. Usual default settings of about one minute or less might be too low, especially when fetching large emails.
The POP3 protocol does not have server-side tracking of which mails have already been retrieved. Generally, a mail client retrieves a mail and deletes it on the server afterwards. However, if the client is configured to not delete mails, then server-side deleting is omitted and the client keeps track of which mail has already been fetched.