SMS and MMS

i am trying to send an SMS message to someones phone who is not a mint mobile user. I sent a message to my email and got [email protected]. I tried sending it back to my phone and it did not go through... I have tried me@tmomail and that does not go through to my phone... I have had no luck sending a message to the AT&T person using their number(at)txt.att.net with no luck... Any help will be appreciated...