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

"Bron Gondwana" <> Wed, 27 February 2019 04:17 UTC

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Date: Tue, 26 Feb 2019 23:17:09 -0500
From: "Bron Gondwana" <>
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Subject: Re: [Extra] Is this a plausible IMAP extension ?
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This isn't a standard feature on any IMAP server I'm aware of.

I can see how to implement it in Cyrus IMAPd. Add a custom numbered ACL to control a set of listed flags, and allow the delivery agent to have that ACL.

On the other hand...

We do something like this already at FastMail, and here's the thing.... the user should be allowed to add or clear this header to change the interpretation of the email in their mailbox. Once they have the message - they should be able to update the BIMI status.

This is particularly important when you're talking about importing and exporting email between systems. Having the flag to avoid phishing, sure. But restricting MUAs from setting that flag - that's bogus.

I guess I'm going to the BIMI session.


On Wed, Feb 27, 2019, at 14:06, 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.
> Does existing IMAP software have this kind of privileged flag? Is it 
> something that would be reasonable to implement, e.g., is there already a 
> concept of users at different privilege levels manipulating the same mail 
> store beyond just R/W and R/O? The IMAP software I use is Dovecot, where 
> in the vast amount of badly organized documentation I don't see anything 
> like this, but maybe it's hiding and I don't know where to look.
> Advice from actual IMAP experts welcome.
> Regards,
> John Levine,, Primary Perpetrator of "The Internet for Dummies",
> Please consider the environment before reading this e-mail.
> PS: If as I suspect this is unlikely to be implementable, I have an 
> alternate approach that involves misusing DKIM.
> _______________________________________________
> Extra mailing list

 Bron Gondwana, CEO, FastMail Pty Ltd