Why is my LG phone unable to send more than a couple photos at a time via email?

Question: My phone's a NON-smart LG from AT&T, and I didn't know it needed a memory card before I took a bunch of photos, so I'm forced to e-mail them to myself one at a time. Most of them go ok, but for some I get an "unable to send" message. If I wait until I'm sending the next batch, the problem ones seem to go through. Any idea why?