I encountered the following situation: Person A writes me an E-mail. The conversation is grouped such that it shows all recipients that were ever included in previous mails as additional recipients as current recipients of the entire thread. I get confused why Person A included those additional recipients (even though the mail was directed only to me but was for some reason grouped with the mails that were to me and the other recipents).

The current conversions grouping is just broken. Why not use the `thread-index` in the email header to group actual conversations instead of fuzzy matching subject and pulling in seven year old unrelated emails or deleted emails into a conversation?

Conversation view enabled me to migrate from Gmail to Proton. I pay for it but it is still broken and not on-par.

I have emails by different people/organisations being grouped because they have the same short subject.
This likewise results in the carefully crafted labels that should be different, to show merged into one conversation.

- and on the other hand -

I have multiple people reply to the same email thread, and they do not show up as one conversation.
This likewise results in each of those conversations being oncomplete.
This likewise results in each of those conversations not folding as expected, showing lots of duplicate information.

Ofcourse I started looking for a "split from conversation" or "merge into conversation" button to fix the conversations/emails I selected. I was hoping to help Proton learn with bigdata eventually, and resolve my immediate problem, but this feature does not exist.

I very much agree. Messages having a common sender and subject is very common for things like order confirmations and invoices, but they are distinct messages and shouldn't be grouped together. However, I don't want to disable conversation group since it's a very valuable feature for actual conversations.

I'd hope that there is a way to group conversations using more unique values, perhaps in the message headers. At a minimum, have options to put an age limit on grouped conversations or allow the ability to exclude items in Trash from being grouped.

"I concur. When using email services for business purposes, you often receive (and send) emails with similar subjects that are otherwise unrelated. This is especially true if you do sales via email. In my case, I send approximately 10-20 emails a day to different clients, all with the same subject.

Right now I am forced to use a third-party email client (and Mail Bridge) to be able to differentiate conversations easily, which in several ways disrupts my workflow.

I understand that the reason for Proton's handling of conversation grouping is that you don't read the body of the emails (as stated here: https://proton.me/support/disable-conversation-view).

However, this shouldn't prevent the addition of an option in Settings to restrict the grouping to conversations that have both the subject and the sender/receivers in common.