This API version isn't the latest one.
It is advisable to use the latest API version which contains the latest Context.IO enhancements.
GET https://api.context.io/1.1/imap/accountinfo.json
The email address of the account you want to get data from.
The response is a hash with the keys id and emails:
{
...
data: {
id: (string) Unique ID of the contact's Context.IO account,
emails: (array) List of known email addresses of associated to the account
}
}