We currently have an Exchange 2003 server and have a few users on MAC using Windows Mail with their accounts setup as IMAP accounts.
This was working fine but had an issue where someone used the server as a relay and was blocked by our antispam provider - Messagelabs. We then locked down the server to allow just the messagelabs IP addresses on the server.
How ever I am now not able to send emails via IMAP but I can receive emails. This is the same on Outlook too so its not just a MAC issue.
I have a user account set up on my Outlook and get the following send\receive error - Sending reported error (0x800CCC0F) : The connection to the server was interrupted. If this problem continues, contact your server administrator or internet service provider.
The firewall has the IMAP port open as I am able to receive just not send.
Is there anything I need to set up on exchange to be able to send using IMAP and not leave the server open for replay from unauthenticated users?