We are pretty new with NetSolutions and I have sent a few email blasts to the registered alumni who are in RE as Constituents.

I had a request to send an email blast out through NetSolutions, but instead using a list of email addresses that are stored in Excel. 

Can I use an external source (Excel) to do email blasts or do the individuals need to be set up as constituents?

You really should look at the knowledgebase first, as there's a wealth of information there, including this:

Thanks.  I generally like to use this resource first, as I usually tend to get helpful and friendly responses from other users.  More often than not, creative solutions are shared rather an black and white restrictive answers.

I agree that this is a great resource, but sometimes the final answer is restrictive; whether it comes from the kb or from a user.  I try to use the kb first and if I don't find a definitive answer, then I'll ask the users for any workarounds they may have been successful in implementing.

Enjoy the weekend.