I know this can be done ... but I'm not exactly sure how. Let's say we have 3 columns.

Column A contains names which are not unique.
Column B contains a code to indicate, in this case a source for the data.
Column C has the data that needs to be summed...

I have used =sumif(A1:A50,"Joe Smith",C1:C50) - but how do I get it to add only Joe Smith's cells in column C when the letter E is in column B?

It's driving me crazy...