Gwabbit has added a cool new feature to their app in the last few days which notifies you if you close an email before adding the contact to your address book. Gwabbit will add an item to your inbox with the contact name asking you to add it. You will also get a counter/indicator on the top of the screen that says how many contacts you have not added.
NOTE: The free version of Gwabbit still sends out annoying unsolicited SPAM to all of the contacts confirming that you have added them as a contact using Gwabbit which they have to opt out of receiving. If you don’t want to annoy the hell out of your contacts I would recommend purchasing the premium version of the app or just avoiding it altogether. Also remember there is an inherent security risk in using such an app since it sends all of your emails to Gwabbit’s servers for parsing which might violate your companies policy especially with confidential emails.