While developing Tinymail, a library for writing E-mail clients, I was convinced that the storage of the summary was something Tinymail itself must handle. Back then there was, even pragmatically, nothing that could cope with the requirements of E-mail on mobile devices for this task.
Meanwhile I got the opportunity to work on the Tracker project. Using the Nepomuk Ontology, I made sure that the message ontology that Tracker uses can actually handle these requirements. I believe that the adoption of Nepomuk and SPARQL evolved Tracker from something that isn’t useful for E-mail software to something that should be involved when writing a desktop service for E-mail today.
I believe such a desktop service for E-mail should:
- Download metadata by getting and parsing ENVELOPE and BODYSTRUCTURE using the FETCH programme of an IMAP server. As explained in this document.
- Give priority to downloading metadata of those E-mails nearby the user’s scroll position.
- Use IMAP’s pipelining. It gives the user the feeling that his technology operates faster than his human brains, even when on high latency connections like GPRS.
- Cache the information, using Tracker’s Nepomuk Message Ontology as schema.
- Make it possible to fetch just one particular MIME part and not the entire messages.
- Enable it to create a new message, consisting of individual MIME parts.
- Make it possible for those MIME parts to have their source in existing messages on an IMAP server when creating a message. When the IMAP server supports CATENATE, it should be used for this purpose.
- Make applications use SPARQL with Tracker’s NMO to query metadata about E-mails.
- Provide a stream API to get access to the the actual data of individual MIME parts. If not cached, the service should download the MIME part on demand. The DBus Stream API should look like GInputStream. Except for read(): I think for the transfer of the chunks of data that Unix Sockets or named pipes are better than using D-Bus.
To this I would like to add that although many people falsely believe that E-mails are like files, E-mails are more like recursive directories (container MIME parts) with items: the E-mail’s MIME parts. Any API that doesn’t admit this, is incorrectly designed.
This goes all the way up to the protocol, where you fetch per MIME part. You don’t fetch entire messages. You can indeed do that but that doesn’t mean it isn’t wrong. IMAP is not POP3. It’s also better to design for IMAP, than to use IMAP as a POP3 service. Better have hacks to support POP3 in your model (I’m serious).
Please don’t make the same mistake nearly every newcomer of E-mail solutions makes. There’s plenty of rubbish already, seriously.