Symptoms

1. The issue started from Confluence 3.5 of which the "Share" feature was introduced and it affects both fresh and upgraded instances.
2. Share and Mail Page functionality overlaps when both plugins are enabled.
3. Either "Mail Page" or "Share" feature can work properly at a time.

Diagnosis

Scenario 1 (Fresh Installation)

1. Install a new Confluence 3.5.1.
2. Install Mail Page Plugin 1.12 and configure mail server.
3. Mailing a page in HTML format will work as normal but sharing a page will not. The shared page will be sent to mailbox but the title and content were not visible and the formatting seems like as if it was from mailing a page:
   
4. To make the "Share" feature to work, disable and enable again Mail Page Plugin or Share Plugin.
5. Sharing a page will then work but mailing a page in HTML format will not work. Send & Cancel buttons were not visible and the formatting seems to originates from Share function:
   

Scenario 2 (Upgrade Instance)

1. Upgrade Confluence 3.4.9 (already installed with Mail Page Plugin v1.12) to 3.5.4.
2. Mailing a page in HTML format will work as normal but sharing a page will not. The shared page will be sent to mailbox but the title & content were not visible and the formatting seems like as if it was from mailing a page:
   
3. To make the "Share" feature to work, disable and enable again Mail Page Plugin or Share Plugin.
4. Sharing a page will then work but mailing a page in HTML format will not work. Send & Cancel buttons were not visible and the formatting seems to originates from Share function:
   

Workaround

Disable and then enable again either the Share Plugin OR Mail Page Plugin from Universal Plugin Manager (UPM).

Resolution

Upgrade to Confluence 3.5.9.

If upgrade is not an option, do the following:

1. Download the attached share-page-1.8.jar from CONF-22834.
2. Upload share-page-1.8.jar file manually from UPM.
3. Stop Confluence.
4. Restart Confluence.