Mail always displays last part of multipart/alternative message

Number:rdar://45838186 Date Originated:6 November 2018
Status:Open Resolved:No
Product:Mail Product Version:1.3.2 (iOS), 11.5 (macOS)
Classification:Bug Reproducible:Always



When Mail displays an email that contains data in the multipart/alternative format (as described in RFC 1521, section 7.2.3), the app currently has the following behaviour: the last part inside the email is always displayed regardless of Content-Type it has set.

However, per the specification, the email client is expected to ignore a format that it doesn't recognize or can't display. For example, if the last part is in the "text/x-whatever" format, this means the sender prefers this format, but the client should only display it if it can display "text/x-whatever". If not, it should revert to one of the previous, less preferred formats (one of which is usually text/plain or text/html).

Steps to Reproduce:

Send a multipart/alternative email containing the following formats in that order:

Expected Results:

The text/x-other part is ignored because the text/x-other Content-Type can't be displayed and text/html (second preferred format) is displayed instead.

Actual Results:

On iOS: The text/x-other part is assumed to be text/html and is displayed instead. text/html part is not displayed.

On macOS: The text/x-other part is displayed as plain text. text/html part is not displayed.


On iOS: Mail version 1.3.2, iOS version 12.1.4

On macOS: Mail version 11.5 (3445.9.1)


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