how to search msg in gmail api code example
Example: query for new messages using gmail api
GET https://www.googleapis.com/gmail/v1/users/me/messages?q=is%3Aunread&access_token={YOUR_ACCESS_TOKEN}
GET https://www.googleapis.com/gmail/v1/users/me/messages?q=is%3Aunread&access_token={YOUR_ACCESS_TOKEN}