Showing Message List

After selecting a mailbox, clients usually show a list of messages. Usually the list contains at least message sender, date and subject.

Most clients simply fetch the wanted message data for all messages and then display them in a list. This is very annoying to use when opening a large mailbox for the first time. Suppose your mailbox had 2500 messages and you tried to open the mailbox for the first time with your laptop's mail client using a 8kB/s GPRS connection. FETCH 1:* (ENVELOPE INTERNALDATE) command could easily send over a 1MB reply (my 2520 message INBOX sent 1,1MB), which would take over two minutes to download. Your user most likely just wanted to check if there were any new messages. Is it really necessary to wait for 2 minutes for that?

A well behaving client would first fetch only the messages that are visible in the message list. Only after they're visible the rest of the mailbox list could be downloaded on background. And by background I mean that user should be able to open messages and perform other operations without waiting for the whole mailbox list to finish downloading. This can be done by fetching data in smaller blocks (e.g. 1:100, 101:200, etc. instead of 1:*).

It might even be useful to not download the entire message list at all. Data connections can still cost per downloaded megabyte. This can be easily implemented by having your mailbox list filled with empty or "message not downloaded yet" stubs. When user scrolls the mailbox list and stubs become visible, the messages are downloaded and the stubs are replaced with the real content. The client can of course anticipate this and always have the previous and the next pageful downloaded so user would rarely see the stubs.

What to FETCH?

You should basically fetch only the information you need, but try not to fetch anything that is costly to servers. Below is a list of fields and how costly they usually are for servers:

Dates

Some people want to sort messages by their Date: header, others want to sort messages by when they were received (INTERNALDATE). You should let the user choose this, and if user doesn't care about the received date, don't bother fetching INTERNALDATE.

Attachment Icon

Many clients wish to display an attachment icon in message list. Instead of fetching the entire message body, you can fetch BODYSTRUCTURE and see if it contains fields that identify an attachment.

ClientImplementation/MessageList (last edited 2009-03-15 22:47:45 by localhost)