Email threading bug: Serious

There is a huge bug with email threading. Today I replied to emails from years ago because of this caused some havoc:

I have a group of emails, some are in the same thread based on subject (Contract) and replies (RE:Contract) There are different people in the To & CC fields. The sales department is sending emails to different clients with the same subject: Contract. They reply back and it gets RE: Contract.

Today I received an email with the subject RE:Contract. This was in answer to a completely different set of To & Cc fields.

Email list = the list of emails in the middle, you know all the emails in the folder list
On the email list this email got grouped under another Contract / RE:Contract group.
On the email list what shows up is the other group’s To / Cc list with the subject “Contract”

I clicked the item and saw a list of threaded emails on the emails view. Thinking that a new Reply was posted for the Contract thread from the other thread (oldest one) but when I looked at the To & CC list people were different and I didn’t reply.

But this morning I made that mistake and replied to a person’s email from ages ago. There is a fundamental bug with the email threading concept.

I can share the screenshot on private, please email me so that I can send you the screenshot to elaborate on what I am talking about.

Hello Icy,

We’re sorry for the inconvenient situation. The Conversations view should group e-mails by their Email ID, but sometimes an issue can occur with older or imported messages. This will not happen with messages that are received through eM Client. Please feel free to export these messages into .eml (right-clicking the message -> Save As) and send them to with a link to this thread and the screenshot, we will look into what the issue is.


well, these are business related and contain sensitive information that I am not at liberty to forward around :slight_smile: so email grouping is based on a proprietary GUID that EM client is setting? well at least that is a relief to know that grouping is not based on subject + sender + receiver grouping (which never made any sense to me anyway)

I will keep an eye out for this then. I cannot imagine an easy solution to this problem - I have a lot of imported emails (20K+) for the time being I turned off conversation / thread view.

thank you maurice

Hello Icy,

It is primarily based on the Message-Id/In-Reply-To/References headers of the email messages, which provide a reliable way of tracking the replies and which were used by email clients since the late 1990s. In case we can’t find a conversation based on this information (because we didn’t download the other relevant messages in the conversion or they are missing) we fall back on a set of heuristics that is based on the subject + sender/receiver.

We are continually working on improving the heuristics to prevent incorrectly matched conversations, which sometimes happens during the initial account synchronization.