Suppress email on message by message basis?

Hi… just returned to Mass Messaging now I have upgraded my PHP version to one that works with it.

A feature request (unless you tell me a better way): Could we have an option to suppress the sending of the emails for a particular message?

Rational: From time to time I want to send messages/advice to my users about, say, how to make good use of the site or avoid pitfalls. But I don’t want to bother them with emails. At present I can send an ‘all users notice’ which appears as a banner at the top of every page until they dismiss it. ( Many of my naive users never seem to so, struggling on with the banner obscuring the page!) But the next message replaces the previous one and hence earlier messages get lost. It seems to be that, with the requested feature, I could place a message in everybody’s inbox to be discovered by those competent enough to do so.