[MlMt] Gmail stars vs flags

[Bill Cole]

On 8 Dec 2017, at 10:34, Robert Brenstein wrote:

> On 29 Nov 2017, at 15:20, Benny Kjær Nielsen wrote:
>
>> Two of my problematic services are running on Exchange. Another is 
>> using office365.com. Yet another is running CommuniGate Pro which 
>> supports the IMAP tags but they decided to allow only a subset of 
>> standard tags (I am arguing with them but no luck so far — large 
>> institutions have their own ideas what should be).
>>
>>
>> Exchange is unfortunately one of very few IMAP servers not supporting 
>> IMAP keywords.
>>
>> --
>> Benny
>
> I had a few exchanges with the people running the CommuniGate Pro 
> server. It seems that they actually do not restrict the usage of flags 
> after all.

I ran CGP servers for almost a decade (through June 2017) and can 
confirm that that recent versions of CGP support all of the core 
standard flags, a fixed subset of the registered commonly used flags, 
its own unique set of special-purpose flags, and 3 generic flags that 
clients can use for whatever semantics they like (making the MM 
tag<->flag mapping helpful.) So compared to servers like Dovecot which 
support ad hoc user-created flags, CGP's support is restricted.

Details: https://www.stalker.com/CommuniGatePro/Mailboxes.html#Flags

Note that flags starting with \ are part of the core IMAPv4rev1 
specification, flags starting with $ in principle have a fixed meaning 
across servers (there's an insufficiently-used IANA Registry,) and any 
others are user-defined. Unfortunately CGP (like Apple Mail) has defined 
it's own bespoke set of $* keywords that are not registered. It also 
uses Junk/NotJunk as a strict binary (which should be "UNJunk" by the 
IMAP naming model...)  rather than the registered trinary model for 
$Junk and $NotJunk as independent but mutually exclusive flags.

> My testing shows that the standard flags are working as expected but 
> custom flags (tags in MM) are not — I mean they are not transferred 
> to another computer. They wrote that CGP supports custom flags 
> $Label1, $Label2 und $Label3  (only 3?).

As of CGP v6.1.16 that was true. I have backed up messages with $Label1 
(mapped to a client name in MM) set on both of my Macs, so I'm certain 
that at least 1 of the 3 worked for me with MM & CGP within the past 
year. Given how CGP implements flags for its file-per-message storage 
model (which is highly accessible to 3rd-party tools) I would not expect 
them to support arbitrary user-defined flags any time soon.

One problem in the CGP world complicating the problem is that the 
licensing model encourages sites to stick with older versions 
indefinitely even though only the current x.y version gets any sort of 
support, enhancement, or bug fix work. As a result, there are far worse 
problems than weird IMAP keyword support frozen in place on obsolete CGP 
systems still being used. I'm not sure exactly when CGP got the fixed 
keyword support it has but I vaguely recall that 4.x (which still exists 
in the wild) only supported the core standard flags.