Are you saying that your "Sent" messages folder doesn't have messages you've sent/replied to? If so, that's been previously asked and answered just a few topics down from this one:
/nlg/index.php?topic=6282.0If you're saying that you don't have a "Sent" folder at all, I'm not entirely sure what to tell you -- I don't think that can be taken away by user level, but I'm not 100% sure.
Per
this post, your account is limited to a total of 10 messages. If you have 10 messages in your inbox, you won't be able to receive any messages, and likely can't save any outgoing messages, either. I'd delete any unnecessary messages to see if that resolves your issue.