I have a raq using the e-mail server that comes with it. I use it from inside my network and from home. I've never had a problem. I must send and recieve a few hundred e-mails a day. I have 2 clients that say the get a relaying denied e-mail back when they are trying to send. Is the problem on my end or on their end? I'm guessing it's on their end, but how do I fix the problem?
are they getting the error please check your mail first? if so they need to authenticate with server before being able to send mail. Remove anything from the outbox, click send/receive, create new message and try to send, if it fails...what is the message in /var/log/maillog?
Basically they need to check their mail before sending. Some mail clients may 'leave' the messages in the Outbox until they are manually resent, but it isn't really a serious issue.
Spammers taking over your box would be a lot lot worse.