We all want messages to be relevant. But what is a relevant message?
Should we consider content and quality? Channel? Format? Probably. But what is more important is what happens afterwards.
From a senders perspective, say company ACME, it could be like this:
A relevant message will trigger the receiver into an action that will create value for ACME. Maybe buying its product? Hiring their consultant? Letting a brother play in the team?
An unrelevant message do not trigger an action that leads to value for ACME.
From the reciever perspective we have this instead:
Here the relevant message is the message that triggers the action that gives the receiver most (or more) value.
@lawlesz suggests that time necessary to process message also influence higher relevance. Less time means higher relevance.
A relevant message is not really about content or channel. It is more about what actions it triggers and what values follow. What is a relevant message for the sender does not have to relevant for the receiver.
Think of "relevant message" as a verb - creating value. And faster is better.