I would suggest in the general settings having the option to edit the emails to users, so they are not effected on upgrade, for example I would prefer to have the following sent to a user that is due to expire as I do not know where to edit this anyway.
Your ad's expire soon <site title>
Thanks for posting your ad on <Site title> - we hope you've had a great response. Unfortunately your ad will expire soon.
(nice if ad picture and title can show here if not a link to ad)
Check the status of your ad at any time or re-post your ad. Log in to <site title> to find out more.
If you don't need this ad anymore, please delete this ad.
(underline is a link to login page)
The <site title> Team
The administrator has disabled public write access.
Expire Email edit (Feature request)
2 years 1 week ago #4452