We've had a couple of problems in the past when two people are editing the same email and they don't know that the other person is in there, so when they come to save what they have done it either doesn't save at all or the other persons' work will overwrite what they have done.
It would be a great to have a lable on the summary page that lets you know who else is working in that email before you start editing.
Example on summary page:
Settings
Channel: Online
Created: 19 December 2014
Currently being edited by: Kate Edwards
Last modified: 30 January 2014
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