How can I enable the pop-up with the question to save the e-mail to ECM? Every time I send an e-mail I receive this message.
The website of the developers doesn't provide anything useful in terms of support and troubleshooting for this add-on. I recommend you to contact them to see exactly what needs to be done, but unless you can't configure the setting in its own menus, then there is nothing to be done.
This is the official page: http://www.ser-solutions.com/products-solutions/ecm-integration/microsoft/outlook.html