Hi Lynn,
There's not a way to wildcard addresses in the way you're describing, however if you're going off of domain names, you could accomplish what you're looking for by assigning those customers to specific companies and then having the trigger perform the action based on the company.
You'll want to create the company to look something like this, making sure to specify the domain so that future customers are assigned automatically to the company:
Once the company is created, you will then want to create the trigger to look something like the below:
Let me know how this works for you. :)