The "Post Office Protocol" is a file transfer protocol which enables an e-mail programme (e.g. Microsoft Outlook) to retrieve e-mails from a mail server. After the e-mails have been transferred, they only remain available on the local computer and are no longer stored on the mail server. A continuous connection to the mail server is not required with POP. If required, the mail programme will establish a connection to the server and terminate it again afterwards.

POP is limited to very few functions, permitting only the listing, collection and deletion of e-mails on the mail server. For other functions (e.g. displaying hierarchical folder structures, simultaneous access to the mailbox from PC and mobile phone, etc.) you must use the IMAP protocol.