MailNews:Minimizing Bandwidth Usage
Make Thunderbird more friendly for unreliable and low-bandwidth conditions.
Thunderbird currently has a number of features that could help in these conditions, such as 'offline folders', 'MIME parts on-demand' and caching. But these features do not always work well in both unreliable and low-bandwidth conditions or when combined together.
This wiki pulls together inter-related issues in one place for discussion and to propose a solution.
User Experience (UX)
The desired user experience in unreliable/low-bandwidth conditions could be described as:
Only download what I ask for and only download it once.
There are a number of bugs/features at the moment that are stopping this from happening, namely bug 405437, bug 345832 and bug 439731. More on these later.
Desired Behaviour
1) Once a message or part of a message (MIME part) has been downloaded it should always be stored locally:
- in offline storage if folder is __offline__ and storage rules allow (e.g. diskspace) OR
- in cache
2) A message should always be retrieved from local storage if possible.
Current Behaviour
NOTE: This refers to TB3, however currently the only difference is the new auto-sync feature in TB3.
1) For __offline__ folders:
- If auto-sync is on and message is not excluded (see strategies):
- it is downloaded and stored automatically
- If auto-sync is off or message is excluded:
- All non-inline MIME parts < ~30KB:
- It is downloaded and stored only when viewed
- One or more non-inline MIME parts > ~ 30KB:
- MIME parts are downloaded on-demand and cached sometimes (there are constraints such as cache size)
- All non-inline MIME parts < ~30KB:
2) Messages in offline store are retrieved from local storage. Cached MIME parts are retrieved from cache, however large MIME parts (i.e. attachments are rarely cached)
NOTE: Effectively this means that messages with large MIME parts (i.e. attachments) are not cached and not available offline'.