Last night and earlier today I was downloading ringtones and e-mailing them to my cellphone. It worked great. Now tonight it won't. It keeps saying MESSAGE DELIVERY ERROR. I tried sending them to my mom's cellphone.. same exact thing. I tried sending ringtones from my father's cellphone to both our cells..same thing..
Is it one particular ringtone that won't go through? Ringtones from one particular site? Perhaps your inbox is full? Check your phone's internal memory. Ringtones generally need to be 30 seconds or less, and attachments kept under 500kb in size.
Is there some common factor in the ringtones that give an error? Size? Source? Just trying to jog your thinking to see what may be causing the glitch....
Another factor may be the network....temporary glitch....and it will start working again. Who knows?