I currently have Zimbra Open Source edition installed on a local mail server in my company. Recently, a couple of my users have reported getting too many spam emails on a daily basis. When I checked, I saw that Anti Spam is very much active so cannot understand why this is happeneing and advise them to continue to train the server by marking those messages as junk.
Those users has no luck and therefore the complain made its way to the upper management and I was asked by my boss to write a report and compare Zimbra with Sendmail and MS Exchange and tell him:
1) Pros and Cons of each
2) Costs involved with migrating to MS Exchange
3) Advantages of using Zimbra
4) If folks will get less spam if we migrate to MS Exchange
Any help would be much appreciate it.