问题
How can I create a Gmail addon? I don't find any API to do it.
回答1:
You can however add scripted gadgets to the sidebar, or triggered by email content:
http://code.google.com/apis/gmail/
回答2:
Gmail finally supports ADD-ONS now in Oct, 2017.
You can read the documentation here - https://developers.google.com/gmail/add-ons/
This Add-Ons will work on Gmail web-app and Android App. iOS support should come soon.
But still you can't publish your Add-Ons yet as mentioned here - https://developers.google.com/gmail/add-ons/how-tos/publish
Support to publish should come soon, however you can still develop and test for that early mover advantage.
However you can use few which are already published - https://gsuite.google.com/marketplace/category/works-with-gmail
回答3:
Google has recently introduced add-ons for Gmail (probably on Oct, 24 2017). It can be developed with Google Apps Script. Google's documentation says
What Gmail add-ons can do ?
Displaying additional information for the user in the Gmail UI. Connecting to non-Google services, to retrieve information or take other actions. Providing an interactive interface to allow the user to control the add-on or send information to another service.
As of now, Google is not allowing to publish new add-ons however they will allow it in future.
While a few add-ons have been made available in the G Suite Marketplace for users to install, it is not currently possible to publish your own add-on to the Marketplace.
How can you publish your own add-on ?
As of now (26th Oct, 2017), they consider it on request basis. If you have a cool idea, fill this form to let them know about it. You will get notified once they accept your listing.
Here is how the add-on interface looks like inside Gmail
来源：https://stackoverflow.com/questions/3436068/how-to-create-a-gmail-addon