When you need to include a custom variable in the send mail behaviour you can do it like this:

Lets say you custom variable is $old_date

$old_date is not available as a dynamic variable of the extension so clicking on the lightning bolt will not help
You need to type it in manually and in the following format:

Your text {GLOBALS.old_date} some more text.

Although we try to ensure all the articles submitted are valid it is your responsibility to make sure you have backups before you use these suggestions on your pc or websites.
We do not take any responsibility for any data-loss, loss in functionality or any problem that might arise in what-ever way or form by making use of the information on this site.