Interactions between email servers and users are governed by email protocols.  The most common incoming email protocols are POP, and IMAP.  Most email applications/programs support one or more of these.  This article is to help users understand and choose which protocol should be selected for each user’s situation.


SMTP (Simple Mail Transfer Protocol) is the protocol used in sending (outgoing) emails. SMTP is the protocol always used for sending (outgoing) emails.


POP (Post Office Protocol) and IMAP (Internet Message Access Protocol) are two different protocols that do the same thing differently. They are both used in receiving emails from a mail server and can both are available for standard and secure (?) connections.

POP (Post Office Protocol):

POP is an email accessing protocol used to download emails from a mail server. Applications like Outlook and Outlook Express using POP will download all emails from the server to the user’s computer, and then delete them on the server. Generally POP server uses port 110 to listen to the POP requests or securely using SSL (Secure Socket Layer) (?) POP uses port number 995. The POP protocol assumes that there is only one client/computer that will be connecting to the mailbox. Even though there is an option in most mail applications to leave the copies of the emails in the server, it is not generally used due to various reasons.

IMAP (Internet Message Access Protocol):

IMAP is another email accessing protocol however it is used to access the mails from the server itself. Applications like Outlook and Outlook Express using IMAP will synchronize a copy of the mail on the server to the user’s computer. All mail data is kept on the server as well as the user’s computer until they delete mail. IMAP server listens on port 143 for incoming requesting to synchronize emails or securely using SSL (Secure Socket Layer) (?) IMAP uses port number 993. Basically, using IMAP protocol means that emails will be stored in the mail server and could be accessible from any clients anywhere if they all use IMAP.

SSL (Secure Socket Layer):

SSL creates a secure, encrypted connection between your email application and the email server. If SSL is enabled, all email connections between your computer and the mail server will be encrypted when you read, download/receive, and send email. This is the same technology you find when using online stores or banking websites which show that you are connecting securely.

Differences Between POP and IMAP

  1. POP downloads the mails in to the user’s computer; IMAP keeps email on the server and provides view from multiple places simultaneously.
  2. POP uses port number 110 while IMAP uses port number 143.
  3. POP downloads mail and disconnects from the server. IMAP stays connected for a longer period of time and is able to send notifications as new mail arrives.
  4. All the email folders and data are in the server in IMAP, using POP email is downloaded and stored in the user’s computer.
  5. In IMAP, changes made (i.e. marking a email as read, as forwarded) are synchronized to the mail server so they are visible from any IMAP client whereas in POP once you have downloaded the email to a computer, no more access is available from other devices.
  6. There is an option in POP mail applications which you can set to leave the mails on the server for certain period of time and then delete. If you are using 2 computers, and one is set to download mails from server and not leave copies, this will delete email from the server even if an additional computer is set up differently.

Backups / Email Loss

There is always the possibility that either the user’s computer/device or the mail server may crash or lose its data. If using POP, a backup of all email should be made regularly and often and saved securely outside of the computer and server. If using IMAP, email should be able to be recovered from the server in the case of a computer crash, however, a backup of all email should be made regularly and often and saved securely outside of the computer and server. Backups to a separate system, CD, or hard disk will help ensure email data is not lost.  UK2 and ANHosting do maintain backups of all servers, but only for a few days at most and may not contain the correct data if too much time has passed.