Dovecot and Apple's Mail.app not playing nicely?

[Gerald Galster]

>>> On 3 Sep 2019, at 15.30, Coy Hile via dovecot <dovecot at dovecot.org> wrote:
>>> Hi all,
>>> Is there anything cute one has to take into account when using Dovecot with users of Apple’s Mail.app?
>>> Behavior I’m seeing is that if I delete or move messages via Webmail (Roundcube, Horde, or even ActiveSync
>>> via Mail.app on my phone), they do get moved or deleted.  However, if I take the same actions in the desktop
>>> mail client, when logging in to the Webmail (or phone) app, I see the messages still seeming to be in the Inbox.
>>> Is this known behavior? A peculiarity in Apple Mail?
>> I am using Apple Mail.App in Macbook, iPhone and iPad. And in fact
>> quite many of us internally are doing the same
>> and I can't see that behaviour. Mail.App correctly obeys \Deleted flag
>> and does not show the mails in folders.
>> Sami
> 
> That's exactly the converse of what I'm seeing. Mail.app sets the \Deleted flag, or flags a message as Junk
> and moves it to the Junk folder. But when I login via, say, Roundcube, it still shows in the inbox, though
> greyed out with a little (/) icon (which I assume is the deleted flag.)  If I move or delete the message via
> the webmail client, it actually gets moved to Junk or Trash. (Or wherever I moved it.)
> 
> FWIW, I think this applies only to deleted messages (where Mail.app may just set a flag rather than actually moving
> the messages to Trash) and to Mail.app's own Junk processing. (Things flagged as Spam and moved to Junk via Sieve do
> end up in the Junk folder.)

Apple Mail does not show messages anymore when the \Deleted flag is set. They are moved to trash only if a mailbox
for deleted messages is set in preferences. Usually they are removed (expunged) from the server a month later.
Roundcube on the other hand displays \Deleted messages greyed out (strikethrough in some versions) by default.

The ability to just mark messages as \Deleted is a nice feature. Imagine deleting 100000 small statusmails without
unnecessary i/o. It may stress your disks (local and server) when that many mails are moved around before being expunged.

Best regards
Gerald