As an OPTION the user can configure - sure.
As default that I can’t change? No, definitely not. It’s very annoying if someone replies to an email from a mailing list and sends that reply to every participant. Example: Class reunion emails, where dozens of people reply “I’m coming” (or not coming) and I get spammed with each + every reply even though I wasn’t the original sender.
IF it gets implemented it definitely needs to be something each user can set or not set as default.
Fair enough, my personal preference intervened. I actually meant to have it as an option (as I wrote last year).
Since last year … still nobody managed to make an option for it. WOW! Didn’t realise it was so complex (of course I am spoiled by Thunderbird) …
Or maybe no-one else wants the change enough to work on implementing it?
I thought this was now a Mozilla or Thunderbird project. Thunderbird has long had this option.
That doesn’t mean that features somehow now magically leak into K-9 Mail from Thunderbird via osmosis. They are still compiled from completely separate codebases. Until someone writes code to implement the feature that you want, it has no chance of appearing in K-9 Mail.
Given the consistent conversation on this since last year, it feels safe to say there is demand for it. The tricky part is gauging that demand, and tracking it in a place where the wider community and core team can see it and engage in the discourse.
I definitely encourage you to post this feature request on Mozilla Connect so it gets more visibility. I recently added a Thunderbird for Android section: Ideas - Mozilla Connect
We do want to evaluate the message reader interface, and this would be considered as part of the that process.
That’s why our implementation of Rust is so important! In the long run, it will allow us to share features between Thunderbird desktop and future versions of Thunderbird on Android.
[quote=“linkp, post:26, topic:6766”]
That doesn’t mean that features somehow now magically leak into K-9 Mail from Thunderbird via osmosis. They are still compiled from completely separate codebases. Until someone writes code to implement the feature that you want, it has no chance of appearing in K-9 Mail.[/quote]
Thank you. As a retired Director of InformationTechnology I always appreciate a good software development tutorial. 
Agreed.
[quote=“j.evangelho, post:27, topic:6766”]
I definitely encourage you to post this feature request on Mozilla Connect so it gets more visibility. I recently added a Thunderbird for Android section: Ideas - Mozilla Connect[/quote]
Yes, indeed. Another seemingly helpful forum I occasionally post in is this one.
[quote=“j.evangelho, post:27, topic:6766”]
I definitely encourage you to post this feature request on Mozilla Connect so it gets more visibility. I recently added a Thunderbird for Android section: Ideas - Mozilla Connect[/quote]
Yes, indeed. Another seemingly helpful forum I occasionally post in is this one.
[quote=“j.evangelho, post:27, topic:6766”]
That’s why our implementation of Rust is so important! In the long run, it will allow us to share features between Thunderbird desktop and future versions of Thunderbird on Android.[/quote]
Yes, the “Rust Revolution” mentioned in the v128 newsletter was enlightening. 
It would be nice to have the Reply all option with a long press on the Reply button, and also to display Cc:'s as Cc: and not as To: x, y.
(K9 version 8.2 for Android)