Reposting my original post:
##Make Activating Accounts Gmail-compatible
Mailchimp-sent double-in confirmations always send with them some metadata.
GMail uses this metadata to display a button (just like you can see on the screenshot) that users can click to automatically activate the subscription/account without even opening the email.
See the the bottom of the email’s source to see the used schemes/metadata.
Also look Google’s documentation about this and a Mailchimp Blog post about the matter.
The only issue I can see with this is that the Discourse activation links require the user to click on “Activate Account”.