Spam comprises approximately 90 to 95 percent of all e-mail traffic on the Internet nowadays, and it is a problem far from being solved. The losses caused by spam are estimated to reach up to $87 billion yearly. When fighting spam, most of the proposals focus on the receiver-side and are usually resource-intensive in terms of processing requirements. In this paper we present an approach to address these shortcomings: we propose to i) filter outgoing e-mail on the sender side and (ii) use lightweight techniques to check whether a message is spam or not. Moreover, we have evaluated the accuracy of these techniques in detecting spam on the sender side with two different data sets, obtained at a Dutch hosting provider. The results obtained with this approach suggest we can significantly reduce the amount of spam on the Internet by performing simple checks at the sender-side.