What INTERNALDATE does dovecot with mbox storage set on a COPY'd message?

[Steinar Bang]

>>>>> Aki Tuomi <aki.tuomi at dovecot.fi>:

> On 09.09.2017 12:33, Steinar Bang wrote:
>> When a message is copied to a folder on dovecot with mbox storage, is
>> the mtime of the saved mbox file set to the time of the save?  
[snip!]
> Internaldate is picked from the separating 'From' line in mbox file.

> "From user at example.org Thu Oct 20 18:44:06 2016"

Sorry! I mistyped: I meant maildir, not mbox.

So, to repeat the question:

When a message is copied to a folder on dovecot with maildir storage, is
the mtime of the saved maildir file set to the time of the save?

Or is the mtime set to the Date: field of the source message that is
saved?

If there is a difference in the behaviour, do someone know the dovecot
version number where the change happened?

The reason I'm asking is a problem reported on the Gnus imap client in
August 2016, where messaged moved by Gnus showed up with the wrong order
and/or wrong date in other imap clients.

(The reason for the different message ordering was that the other clients
use the INTERNALDATE and that was changed to the time of message move
when Gnus was used. Gnus use the Date of the source message)