On 2019-03-06 12:00, James Brown via dovecot wrote:
Have updated our mail server and are now running Dovecot 2.3.4. Things
are mostly working OK, but occasionally I have users on latest iOS
getting this message: “this message cannot be displayed because of the
way it is formatted. Ask the sender to send it again using a different
format or email program. multipart/alternative”
The email seems to open OK on the macOS version of Mail.app.
Also getting “Loading...” displayed in body section of the app with
content never displayed.
Most emails are fine, but just get this strange ones occasionally. Our
previous mail server was much older, with older version of Dovecot,
etc. This server never used to have these issues.
Just wondering if anyone has any ideas or suggestions? Can’t see
anything in the logs.
You are probably seeing the effects of a bug or shortcut in the iOS mail
client.
A few years ago, I was working on system that sent bulk marketing
emails. I had particular problems with iOS and multipart/alternative
messages. iOS would insist on displaying the second of the multipart
components assuming that it was html, without actually checking the MIME
type. For other technical reasons, I wanted to construct the multipart
mail so that the html version body was before the plain text version.
Every other email client I tested worked fine, but iOS broke when it saw
that message.
I also saw problems when iOS mail was configured to only download the
first 32kb of each email (to save on cellular data), but those problems
where intermittent and harder to pin down.
In short, I doubt there is a bug in dovecot, it will be following the
RFCs, but iOS is probably playing fast and loose with the standards.
--
David Pottage
