Learn how to check if an email has been replied to in Gmail using Google Apps Script.
“Gmail doesn’t have a built-in feature to check for replies, but you can use Google Apps Script to create a custom script that will automatically check for replies to your emails.”
Amit Agarwal has shared another practical tutorial for anyone looking to add more intelligence to their automated Gmail workflows. While Gmail organises messages into threads, it does not provide a simple out-of-the-box method to programmatically determine if a specific email has received a human response.
In his latest post, Amit explores the technical side of email headers: specifically how the Message-Id of an original email is referenced in the In-Reply-To and References headers of subsequent replies. This logic forms the basis for his Apps Script solution, which helps developers identify valid replies while ignoring automated clutter.
One aspect I found particularly interesting is the filtering logic used to try and separate human interaction from the rest. The script accounts for several common hurdles as it ignores out-of-office auto-responses, delivery failure notifications, and messages sent from the user’s own account. By checking the auto-submitted header and using regex to filter common bot addresses like no-reply or mailer-daemon, the solution ensures you only track meaningful engagement.
Crucially, this logic is not confined to the Google ecosystem. Because these headers follow standard email protocols, the detection works seamlessly even when recipients reply from external clients like Microsoft Outlook or Apple Mail.
As Amit notes, if you want to use this logic effectively, you should store the rfcMessageId and threadId in a Google Sheet or database immediately after sending. This approach allows you to run your reply-checking scripts at any time without losing the original context.
You can find the full code and detailed header explanations in Amit’s blog post.
