Microsoft Tuesday released details on how Windows Phone 7 users can minimize unexpected surges in data use, and finally identified the cause of these surges: a synchronisation inefficiency between the Windows Phone mail client and Yahoo Mail.

The jumps in data use affect "a very small percentage of users," according to a statement released by Microsoft. In the statement, the company outlined a work-around, pending a formal fix "which will be rolled out in the coming weeks."

Microsoft, which gained a 2% share of the US smartphone market with Windows Phone 7 during its first two months of availability, also described an issue involving its mobile e-mail synchronisation protocol. Mail services from Google or others that use this protocol may have e-mail messages getting hung up in the outbox.

Shortly after the Windows Phone 7 handsets became available, some users were complaining that they were seeing very large, unexpected jumps in data use, for no obvious reason.

According to Microsoft, the data surges potentially affect only those Windows Phone users working with Yahoo's mail service. The spikes are caused by an "inefficiency [that] exists in the synchronisation of e-mail between the Windows Phone Mail client and Yahoo! Mail," according to Microsoft. No further details were given.

Both vendors are working together to fix the problem permanently. Until then, users can change the frequency of Yahoo Mail downloads and the date range that those downloads cover.

Here are the specific steps to change the WP7 settings:

1. On the Start screen of Windows Phone 7, click on the arrow at the top right

2. Choose "Settings" from the app list

3. Choose "email & accounts"

4. Choose "Yahoo! Mail"

5. Click on the setting under "Download new content"

6. Select a less frequent setting. The default setting is "every 2 hours"; Microsoft recommends changing this to "manually"

7. Click on the setting under "Download email from"

8. Select a shorter date range. The default is "the last 2 weeks"; Microsoft says change that to "the last 7 days"

Microsoft Exchange ActiveSync issue

The second problem involves Microsoft's Exchange ActiveSync (EAS) e-mail synchronisation protocol, which is licensed to range of client and server mobile implementations. Potentially, this problem can affect e-mail services that use this protocol, including Microsoft Outlook and Gmail. Again, according to Microsoft, this "may affect a very small percentage of users."

The problem can be triggered by an e-mail that either is bigger than the size limit set by the server or that is sent to an invalid e-mail address. Right now, a user can delete mail that seems to be "stuck" in the outbox. Microsoft plans to have a permanent fix "in a near-term end user update."

Meanwhile, speculation is swirling about an overall WP7 upgrade coming soon.