We should have one type that is used for the "From" information, and it can be used as a default on the mailer or on the individual message. 

e.g.
```go
// Which persona to send mail on behalf of
var Salesperson = mail.From{
  Name: "Rob Fig", 
  Email: "robfig@company.com",
  ReplyTo: "sales@company.com",
}
```