Thanks for your response. I didn't mean the smtp server values but rather custom keys in the appSettings section such as a particular email address to use depending on the site that is currently accessed.
So if I have a single Sitefinity instance that supports 3 separate sites: a.domain.com, b.domain.com and c.domain.com. If I need a specific email address for each one, does Sitefinity provide a way for me to determine which one of the three domains is in context? Does the urlMapping section in the web.config provide any help in this regard? If not what is the recommended way to handle this scenario?