Microsoft Exchange: Mail rule allows regular expressions. But which ones?

Solution 1:

You're right that the documentation there is a little light. However, EAC is just a UI for the PowerShell commands that get run.

So, the real question is "What regular expressions does PowerShell support?"

RegEx is supported and in the case of "The Sender address matches..." this would be a -match expression. So, you could put something like this into that box [a-z]+ to match any character from a to z. This is just an idea to get you going since you didn't say exactly what kind of match you wanted to make.

Solution 2:

You're in the right location...

Just enter a regular expression.
There a handy utility available at: http://regexhero.net/tester/