I have a weird issue here
I have some users who are accessing our exchange mail server 2007 from another office. They are using MS outlook 2007. If they enable the SMTP Authentication feature, they wont be able to send messages, If disabled they can and when they do, our mail content filtering server (MailMarshal) catches all the messages coming from their side to us as SPAM.. here is what SPAMHAUS says about their gateway IP Address:
This IP range has been identified by Spamhaus as not meeting our policy for IPs which should deliver 'direct-to-mx' mail to PBL users.
Important: If you are using any normal email software such as Outlook, Entourage, Thunderbird, Apple Mail, and you are being blocked by this Spamhaus PBL listing when you try to send email, the reason is simply that you need to turn on "SMTP Authentication" in your email software settings (Tools : Accounts : Properties : Outgoing Mail Server : check "My server requires authentication").
If you do not know how to do this, ask your Internet Service Provider for help with "SMTP Authentication".
The strange thing is that others are accessing their mails with outlook 2003 with SMTP Authentication and it is working perfectly.... So far i can't find any proper solution for this!!!