Mail on iOS allows five photo attachments per mail. If you're sending lots of photos to friends or family from a vacation, you'll have to split up your photos among multiple emails. Here's a solution, just in time for sharing those Labor Day snapshots. It's called Instamail Photo. It's free and it works well.
You bring up the app, select your photo roll or a particular album and click to select the photos you want. When you click the "done" button your regular iOS email will appear, with all your photos as attachments. Type in the recipient's name and off you go.