I have noticed that sometimes email from an employee in the company to another employee will sometimes go to the junk folder. This seems to happen when using an email client from a computer at home. Looking at the SPAM information in the header it seems that the problem occurs because the ISP's IP address causes a high SPAM score to be used.
We have an edge MTA in use. Employees must authenticate with it in order to send email. When users authenticate with the edge MTA many of its anti-spam measures are bypassed.
Is there any way to pass to the Zimbra server information that the sender of the email has been authenticated by the edge MTA? Or is there documentation on a better way to use Zimbra and an edge MTA?
Because of this problem I have considered getting rid of the edge MTA. But on the other hand I like having a separate server where I can setup things like F-Prot AV and grey-listing without having to disturb the stock Zimbra configuration files.