I'm a network admin for a small company, and recently one of my users purchased an account with an email marketing company. She is going to use their website to send out a newsletter. When she tried to email the newsletter within our domain, no one receives them. However, when she emails them to @yahoo, @gmail, @hotmail, etc. it works. She received an email about the problem:
<mycomany's mail server> rejected your message
at the bottom of the page:
[mycomany's mail server]#<[mailserver] #5.0.0 smtp; 530 SMTP authentication required> #SMTP#
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