How to politely follow up after contacting potential postdoc advisor?

After sending an unsolicited email to a potential postdoc advisor, and receiving no response for a while, what is a very polite way to follow up?

Based on past experience lack of immediate response does not necessarily mean a lack of interest, they might just have been too busy at the time. This question is about how to best phrase the followup email to be as polite as possible, and not to seem pushy.