I would like to build an application in Google App Engine (Python) that would be fully connected to a single GMail account and then filter e-mails from this account (e.g. filter messages for a certain string and show it on the string). In the future I am also going to implement the option to send messages.
What is the most efficient way to do this (solution provided by Google if possible)?
There is no Api for Gmail in App Engine. The only thing you can do is forwarding messages to App Engine.
I have used fowarding for building auto responders.
But there is an excellent GMail Api in Google Apps Script with lots of functions. Apps scrips uses javascript. And ofcourse your apps script can communicate with App Engine.
Filtering GMail messages in Google App Engine application