Combining Google App Engine and CloudMailIn on Heroku in one setup

Question

I'm developing a web app on Google App Engine, for which I recently decided that it requires a high performance inbound email processing functionality. GAE's functionalities for incoming email are rather limited, however CloudMailIn on Heroku seems to be able to do everything that I want (https://addons.heroku.com/cloudmailin)

Would you consider it a wise decision to run the website, user accounts, and databses on GAE, and run CloudMailIn separately with e.g. an API connection to write to the datastore on GAE? So far I have built all my web apps on GAE, so I prefer to stick with what I know. However if this is likely to bite me once I scale, then of course I will move everything to Heroku. Does anybody have experience with this?

Answer 1

Thanks to answers from Peter and Steve I now understand that both Sendgrid and CloudMailIn can be controlled through a simple webhook, so no need to include Heroku here. FYI I ended up using MailGun Routes because their features had a better fit with my requirements.