Send IFTTT an email at trigger@applet.ifttt.com with a hashtag in the subject (e.g. #IFTTT) and this Trigger fires. You can optionally add a single file attachment (up to 30MB) and IFTTT will create a public URL to the file as an Ingredient.
This Action will turn a WeMo Switch on. If the WeMo Switch is already on, it will remain on.