I have some software I wrote that sends automated notifications to a specific email address. I'd like GMail to group notifications with the same subject line together into a single conversation, but for some reason it is treating each of these emails as a new conversation (i.e. listing them separately in the GMail UI). I had thought using the same subject line would be enough.
Right now, I'm sending emails with no additional special headers. My question is: Are there extra headers I can include in an email (such as a "conversation ID" or something) that will encourage GMail to group messages into a conversation (assuming the subject lines are all the same)?
If not, is there some other condition that GMail uses to group messages into a conversation that I am missing here?