Thank you for reporting this, it has been added to our bugs list.

After looking into this, it seems that IMAP doesn't have a concept for forwarded vs replied. It just sees both as "Answered". In order to be able to mark messages as replied, we have to mark them the same way when forwarded. If we change anything it would remove the functionality for replied messages to show as well. As such, we have decided to leave this functionality how it is since its been this way for years. We will look into why the flag may not be syncing over to EAS though.

Are you sure abot that?

It seems to me (but I can be wrong... To be sure I have to recover an old backup) that before the "Production Ready" Beta the flags replied and forwarded were correct... 

I repeat, I'm not sure, I could remember badly ...

Maybe SM is setting the flag in newer build when it wasn't in older ones?

To support Josh's answer...

We are using the answered flag referenced in the RFC that Alex linked. Since we don't have a way of knowing the difference between replied or forwarded (specifically from IMAP) we assume replied to keep the more common functionality working. I did check and we have handled this the same way in the code since around 2015 or before.

Actually some (most?) mail clients seems to use IMAP keywords, if they are supported by the IMAP server, to keep track of forwarded messages.

A consensus of the used IMAP keyword for this seems to be to use $Forwarded as per RFC5788

Introduction on IMAP keywords:

https://tools.ietf.org/html/rfc5788#section-1 

Specific part about $Forwarded:

https://tools.ietf.org/html/rfc5788#section-3.4.2 

Also from dovecot IMAP server documentation pages:

Of course for this to work both the server and client must support it.

Edit: For example opensource dovecot imap server + opensource roundcube mail 1.4.x webmail, both flags are used to differentiate if a mail has been forwarded, replied or both.

root@mailstore-01:~# doveadm fetch -u test@domain.tld 'uid flags' mailbox inbox 

(answered mail)
uid: 42526
flags: \Answered \Seen

(forwarded mail)
uid: 42528
flags: \Seen $Forwarded

Edit 2:
Outlook (tested with 2019) does not support the $Forwarded keyword and also seems to remove the flag from the mail (on the IMAP server) if you alter the mail within outlook.
I think it only keep track of forwards in it's own local file (when using IMAP)

Kind regards

Hello,

I wanted to update this thread with what I have found since I last posted.

First, to respond to Sébastien Riccio, I wanted to thank you for providing that information. We had already looked into the keywords and come to same conclusion, but it is useful to have the confirmation from someone else.

As for the issue with syncing the flags to EAS, I was able to replicate an issue with this and believe I have fixed it. If this is still an issue in the next version of the BETA please let me know.