When it comes to creating and sending a promotional email, you could in fact create the best welcoming email ever. Having a welcome email is a very critical part of the on-boarding process for all businesses. When you are able to have an amazing welcome email, it may impact the activation rate, help to turn new customers in to life long partners, subscribers into daily readers, and free trail users into fans.
The true goal of any welcome email is to simply guide the user to the next step. Ask yourself how can you show the actual value of your service/information/product as quick as possible?
If you are a twitter user, than this could mean encouraging users to complete their profile. If you are Amazon, it could mean driving new customers to the most profitable products. If you happen to be Basecamp, then it could mean getting people to log in so the product will sell itself.
You have to learn which action will get your users hooked, and build your welcome email around that.