Lemonade Profile
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The Lemonade Profile is a set of protocols and mandatory extensions which provides email access to diverse environments, including mobile handsets and other resource constrained devices. It is the product of an IETF Working Group, and is largely based on pre-existing specifications, including IMAP and the Message Submission profile of SMTP. It was first published in 2006 as RFC 4550, and updated in 2009 as RFC 5550.
Unlike many other mobile email proposals, including Push-IMAP, the Lemonade Profile does not provide for message submission via IMAP, but instead allows the MSA to pull message data directly from the IMAP store in a secure manner. This allows the protocols to continue to leverage the vast body of work on SMTP, and also means that any traditional IMAP client can interoperate fully with a Lemonade service.
Rather than providing a Push e-mail mechanism, The Lemonade Profile relies on the existing IMAP capability to provide short notification messages at any time, and includes support for the IDLE command. When there is ongoing activity between the server and the client, IMAP will automatically inform the client of the presence of new messages. IDLE ensures that the server will inform the client of new messages even when there is no other activity taking place between client and server by ensuring that the connection is not disrupted by a timeout. Because of this, IDLE is often cited as providing a user experience similar to that of Push e-mail.
Other Lemonade features include the ability to forward a message, part of a message or message attachment to another party—without first downloading the relevant message parts to the handset (this involves extensions to both IMAP and SMTP) as well as quick and efficient re-synchronisation of client with server in the event of a broken connection.