... unlike the Gmail app which can use the header information and possibly parse the message to figure out which emails are part of what conversation, Aqua mail can not do this.
"Any sufficiently advanced technology is indistinguishable from magic." Arthur C Clarke
There is no real magic behind thread detection in Aquamail, just a well defined logic (while I suspect GMail server might be using what is called "fuzzy logic", but my comment is not about that).
There are two issues that it looks like are being mixed up, and that's not helping anybody. I thought I explained this in the earlier part of the thread, but maybe it was not clear.
(A) One: there is a well defined case where Aquamail does
not group messages to a thread (but Gmail does/might): The same subject, different senders on the other end, and no "References" or "Reply-To" headers.
And if one disabled the option responsible for this: Aquamail will not group messages that have: the same subject, the same sender, but no "References" or "Reply-To" headers.
(Note, that everything I've seen from Davey126 and everybody else in these forums complaining about thread grouping falls into this category [since the initial quirks have been fixed more than a year ago]. So, your case here is quite likely unique.)
(B)A very different issue that seems to be the case in the example you made above in this thread (
https://www.aqua-mail.com/forum/index.php?topic=5361.msg31829#msg31829 ) is when the headers in question are present. According to Aquamail's logic those messages should have been grouped in one thread/conversation. And that's where I suspect the culprit of
most of your problems might be.
I am actually very curious to hear the result of Kostya's analysis.
So far, I expect it could be one of the following:
1. Something in your server breaks/modifies the headers of the incoming messages. But, AFAIR, you are using Gmail account (right?). In that case, I don't expect such a problem.
2. There is some "zero-day" bug in Aquamail that gets triggered in your case. -- This seems to be very unlikely, but that makes it even more important to find and fix.
3. Some type of corruption of the database.
4. Something totally weird in the device/configuration ...
So with Aqua mail you have to just expect the conversation mode feature will not work ...
Look, I understand that you are frustrated because something does not work
for you. And even if it would've worked for everybody else in the world, what ultimately matters to you is that it does not work
for you. But if you want the issue to be resolved, the hysteria about the issue does not help.
I know that you provided the information requested. So, let's have some patience, while awaiting the outcome of Kostya's investigation.