One single POP and the standard used on TCP/IP networks such as the Internet, receive e-mail (e-mail) communications conventions (Protocol). Users own which establishes the method for accessing mail holds the e-mail you have received new mail checking the receives the email, your email. Download all received in principle to use the POP mail client (mail client), and then deleted from the server on the mail unread folder and read administrative classification. Not suitable if you want to use the email address you can see all incoming mail is connected to the Internet, fewer mail storage capacity of the server, so the same on multiple devices. Tend to use IMAP4 such cases can already read management, taxonomies, or on a server, use the Web mail system. Introduced enhancements to the APOP was done in plain text (unencrypted) user authentication for user name and password for sending and receiving, in the old protocol widely used since the 1980s to encrypt the credentials. The use of SSL/TLS to encrypt entire POP communication, problems have been found in the APOP POP3 over SSL/TLS (POP3S/POPS) is recommended. The standard port number POP2 POP3, TCP 109-110, POP3 over SSL/TLS and 995 is.