“Message cannot be displayed because of the way it is formatted” iOS

[James Brown]

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.

Thanks, James.

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