Way to assign mode?

Way to assign mode?

Is there a way to assign a mode through a business rule? We want to note which service an item came from, but since these items are coming in through email, they're not already part of a new ticket. Rather, we want to assign with a business rule when the item arrives (based on which email address it came from). I see a way to check mode in a business rule, but not a way to assign a mode. 

Is there any way to do this? 
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