Monday May 14, 2007

Comms Suite: Pull or Push, It's Up to You

Doctor Doolittle's pushmi-pullyu (pronounced "push-me-pull-you")

Traditional email access (dial-up) was and still is "pull" based. You log in to your mail server, your mail client polls the server to see if there is new mail, and if so downloads it to a mailbox in your home directory. The same process happens at regular intervals afterwards as well.

The IMAP protocol, in effect, introduced clients to "push" email. Through support for polling and monitoring of the server, the IMAP protocol enables clients to become aware of new messages, fetch message data, and choose to dowload the message. Wireless devices were next to become 'instant-on' email clients, but used proprietary protocols to achieve that state of bliss.

Now the IETF, in the form of the 'Lemonade Profile,' has provided a standard way to use the existing IMAP IDLE command along with SMTP modficiations for push email.

Communications Suite 5 (released March 2007) supports IMAP IDLE (aka push email). Support for the IMAP and SMTP extensions described in the Lemonade Profile, RFC 4550, is planned for the next major Communications Suite release.

The advantages of IMAP IDLE are:

  • Mail clients do not have to poll the IMAP server for incoming messages.
  • Eliminating client polling reduces the workload on the IMAP server and enhances the server's performance. Client polling is most wasteful when a user receives few or no messages; the client continues to poll at the configured interval, typically every 5 or 10 minutes.
  • A mail client displays a new message to the user much closer to the actual time it arrives in the user's mailbox. A change in message status is also displayed in near-real time.
  • The IMAP server does not have to wait for the next IMAP polling message before it can notify the client of a new or updated mail message. Instead, the IMAP server receives a notification as soon as a new message arrives or a message changes status. The server then notifies the client through the IMAP protocol.

To configure IMAP IDLE in Messaging Server 6.3, see To Configure IMAP IDLE.

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