The Broadcast Email method may be used only in rare cases but it can be pretty handy in certain situations. This will require you to enter your client's email in the Broadcast email field in the campaign properties. To find the Broadcast Email field, just open up the properties of the campaign that you want to set up the Broadcast Email for. Go to your campaigns list then click the Actions menu of the campaign then click Properties.
So whenever sending a broadcast, they need to use their email account which was entered in the campaign properties. And the format should be no other be than the following:
--sent to email@example.com
The types available would be EMAIL, SMS and BOTH.
Both means the broadcast will be sent both via Email and SMS to the campaign subscribers. You can also enter any subject for the email. It doesn't matter. What definitely matters here would be the format.
An example would be:
"SMS|Hello this is a broadcast" (without the quotes)
Then once the client sends that to firstname.lastname@example.org using their email account that's entered in the Broadcast email field in the campaign properties, the subscribers of the campaign will receive the message on their phones and the message would be: "Hello this is a broadcast".