Either "Mail Page" or "Share" feature can work properly at a time.

The issue started from 3.5 where "Share" feature was introduced and it affect fresh and upgrade instances.

Scenario 1 (Fresh Installation)

1. Install fresh 3.5.1
2. Install Mail Page Plugin v1.12 & 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 & content weren't visible and the formatting seems like as if it was from mailing a page (case 1.jpg)
4. To make "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 (case 2.jpg)
6. You will need to disable and enable again Mail Page Plugin or Share Plugin to have it work

Scenario 2 (Upgrade Instance)

1. Upgrade 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 weren't visible and the formatting seems like as if it was from mailing a page (case 1.jpg)
3. To make "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 (case 2.jpg)
5. You will need to disable and enable again Mail Page Plugin or Share Plugin to have it work

However, mailing a page in Text format will work as normal except that the sender will always appear as Anonymous (case 0.jpg)