I’m having trouble with email threading when using Mailgun as my email service. When I send emails to my customers, I set a custom Message-ID header. My understanding was that when recipients reply to these emails, Gmail should automatically include my original Message-ID in the References and In-Reply-To headers of their replies.
However, this doesn’t seem to be working with Gmail recipients. The reply emails I receive don’t contain my original Message-ID in these headers, which breaks email threading.
Is this normal behavior for Gmail? Are there any workarounds or alternative methods to maintain proper email conversation threading when sending through Mailgun? I really need to keep related emails grouped together properly.
This is indeed a well-documented issue with Gmail. It often disregards custom Message-IDs assigned from external services like Mailgun, leading to inconsistent email threading. I experienced a similar problem in a previous project with customer interactions. A practical solution I found was to utilize a consistent Reply-To address that you can monitor programmatically. Additionally, consider implementing a custom header, such as X-Conversation-ID, to maintain a unique identifier for the threads. By doing this, when Replies are parsed by Mailgun, you can use that custom header to organize conversations within your application. While Gmail may not display the threads correctly to users, this method ensures your internal tracking remains effective. It requires more effort on the backend, but it puts you in control of email threading.
Hit this same issue with a client last year. Gmail ignores your Message-ID and makes its own, especially if your domain doesn’t have solid reputation with them yet. Here’s what worked: keep your subject lines consistent with threading keywords, and make sure your Return-Path header matches your From domain. Gmail’s way more likely to thread properly when everything’s aligned domain-wise. Also found out Gmail treats emails differently based on how much recipients engage - if people actually open and reply to your emails, threading gets better for those conversations. Timing matters too. Space out your sends instead of blasting them all at once - Gmail gets suspicious otherwise.
Gmail ignores custom Message-ID headers from services like Mailgun most of the time. It creates its own threading logic that doesn’t care what you send.
Had this exact problem building our support system. Mailgun’s great for delivery, but Gmail’s threading drove me nuts.
Switched to automation and it solved everything. Built a workflow that captures all email interactions and handles threading myself instead of trusting email clients.
When someone replies, my system detects it, pulls the conversation context, and updates the thread in my database. Now I get proper threaded conversations in my app no matter what Gmail does.
The automation processes Mailgun webhooks, parses replies, matches them to original messages, and keeps everything organized. Way more reliable than hoping email clients cooperate.
Stop fighting Gmail and build your own email thread system. Gmail’s gonna do whatever it wants with Message-IDs anyway.
I had this same nightmare with our support platform. Wasted weeks messing with headers and domain settings. Nothing worked reliably.
Ended up building automation that catches every email interaction. When Mailgun sends something out, my system logs it with a tracking ID. Replies come back through webhooks and get matched using custom patterns in the subject and sender details.
My automation creates its own threading database that actually works. Tracks full conversation history, assigns proper thread IDs, and handles customers who mess with subject lines or forward stuff.
Now my team sees perfect threaded conversations in our dashboard no matter what Gmail does. Plus it auto-tags everything and routes to the right agents.
Building this kind of email automation is pretty straightforward at https://latenode.com.
yeah, gmail’s notorious for this. they ignore the message-id you set, especially from bulk senders like mailgun. try subject line threading instead - keep the same subject and add “Re:” at the front. it’s not perfect but works better. also check if your emails are landing in the promotions tab - that breaks threading too.
Gmail’s handling of Message-ID headers is frustratingly unpredictable. It really comes down to your sending reputation and domain setup. I worked with a fintech client where Gmail started respecting our Message-ID headers much better after we set up proper DKIM, SPF, and DMARC with strong alignment. The big thing was making sure our From domain matched the DKIM signing domain. We also kept our sending patterns consistent and avoided anything that looked promotional. Threading still wasn’t perfect, but way better than before. Make sure your Mailgun domain is warmed up properly with good deliverability stats - Gmail definitely treats established senders better than new ones.
i had the same prob! switching to a dedicated IP for mailgun totally helped my sender rep with gmail. they really don’t like anythin that looks promotional, so keep your emails super transactional. that should help with the threading too!