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.
Before the mail is sent you'll get the option to compress the images, which could be a good thing because most ISPs limit attachment sizes. Apple does too, but I couldn't find any specifics. It's believed to be 20-25 MB. Gmail has a 25 MB limit.
When I tested the app and sent images full size I didn't see any deterioration of image quality. Compressing the photos results in some loss of sharpness, but it's probably OK for an email. One thing I didn't like is that the attachments are renamed, and they all have the same name, instamailapp. When you save multiple photos your computer will append a "-1,-2, etc." It seems to me things would be simpler all around if the image name was retained.
Despite that quirk, Instamail Photo works and the price is right. The timing is good too, since here in the US it's a holiday and there is a lot of picture taking going on. I've added Instamail Photo permanently to my iPhone and iPad.
Instamail Photo is a universal app, and requires iOS 4.3 or greater.