Re: [Extra] Is this a plausible IMAP extension ?

[Alexey Melnikov <[e-mail]>]

On 27/02/2019 06:32, Arnt Gulbrandsen wrote:

> On Wednesday 27 February 2019 04:06:36 CET, John R. Levine wrote:
>> There is this thing called BIMI that is being debated elsewhere in 
>> the IETF.  Leaving aside for the moment the issue of whether it's a 
>> good idea in the first place, it invents an IMAP feature that seems 
>> dodgy to me.
>>
>> When an MTA that supports BIMI delivers a message into the mailstore, 
>> it adds a header that tells MUAs where to find a logo to show next to 
>> the message.  (Think of it as x-face for corporations.)  Since bad 
>> people could phish victims with their own header with a misleading 
>> image, BIMI invents a new IMAP flag that only the delivery MTA can 
>> set on messages where it has added a virtuous header.  An MUA can 
>> test it to decide whether to show the logo.  Other IMAP or POP 
>> clients can't set the flag, but it presumably stays with the message 
>> if it's moved from one folder to another.
>
> There is a sort of expectation with IMAP that you can copy messages. 
> That you can copy your entire mail archive from fastmail to gmail and 
> the result will work as before. There are programs to do this, 
> imapsync for example, and doesn't one of the big MUAs have this 
> builtin, too?
>
> BIMI wouldn't. With BIMI, the copy would be degraded, not complete.

To expand on this: the answer would depend on whether a particular IMAP 
server supports a particular IMAP keyword or storage of arbitrary IMAP 
keywords. Support for arboitrary IMAP keywords is relatively widely 
implemented feature in IMAP servers, but unfortunately it is an optional 
feature.