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As with priority tag (which I seldom use, but use), a tag 'replace' may be helpful to inform the receiver your previous message should not be read, or may be ignored, or is simply made redundant by the follow-up. (If trusted) the receiver can safely ignore and save some time. If many messages, someone won't have to delve to *a lot* of messages.

Don't worry about Microsoft, it'll follow!

There are many tags available. I think the one that fits your criteria is the "later" tag. Right click on a message -> mark message, and see what options you have. With Kontact 2 I also suspect custom tags will be made available.

The message should be marked at the 'Composer' stage, before the message is sent; perhaps a version number attached to the message may suffice. This works the same as in software versions. It's to inform the receiver that the message sent before this message or follow up contains too many communicational errors.