IssueTracker

Description

I'm using the Google.Apis.Gmail.v1 NuGet package in my .NET application to subscribe to Gmail notifications of user's mailboxes they've given my app permission to read and edit. I request access to the user's mailbox by specifying the scopes:

• "https://www.googleapis.com/auth/userinfo.email"
• "https://www.googleapis.com/auth/gmail.modify",

I've setup a Google PubSub topic in my Google Cloud Console, and I've configured Gmail notifications to be published on a specific Topic. This is working fine. When a user authenticates my app using OAuth 2, after I've exchanged the code for an access token, I use the Gmail API to add a watch on the user's mailbox. This is also working fine.

However, when I receive an event from the specified Topic, I receive an email address and a historyId. When I request the history list with the received ID, I never (actually: NEVER) receive a history entry containing an actual value for the MessagesAdded property. It is always NULL. Sometimes I get a history entry with just one message in the 'Messages' property, but never in the 'MessagesAdded' property. Therefore I can not explicitly determine when the user received an email message. I've tried re-authorizing the application by the user's email account, but that doesn't work. The result is always the same, even though the documentation states that I should NOT use the Messages property, but one of the event-specific lists (like MessagesAdded or MessagesDeleted).

How am I supposed to determine when the user receives an email message? I am only interested in retrieving received messages one at a time, I am not interested in keeping an explicit list of synchronized messages.

Output

An example of the history.list responses I mostly get:

{ "History": [ { "Id": 7569705, "LabelsAdded": null, "LabelsRemoved": null, "Messages": [ { "HistoryId": null, "Id": "191d7c452d92dc7e", "InternalDate": null, "LabelIds": null, "Payload": null, "Raw": null, "SizeEstimate": null, "Snippet": null, "ThreadId": "191d7c452d92dc7e", "ETag": null } ], "MessagesAdded": null, "MessagesDeleted": null, "ETag": null } ], "HistoryId": 7569711, "NextPageToken": null, "ETag": null }

Steps

• Configure Google Gmail API and PubSub
• Setup an OAuth connection and subscribe to Gmail notifications on the Topic
• After receiving a message on the Topic, retrieve the corresponding history list
• Find out the MessagesAdded property is always empty.