Who fights spam in microsoft exchange server?

Question

Microsoft Exchange

The essence of the issue is the following: there is Microsoft Exchange Server 2013, it has been working for 2.5 years. At the very beginning, when spam began to pour in, they turned on the built-in anti-spam, over time, spam became less. But as always, there is a but, the other day a lot of spam began to pour in again and our clients began to complain that our server was rejecting letters. The solution was found to add client domains to the white list, and as if the letters go, but there are still those clients whose existence we may not be aware of, and such a situation with the mail server spoils the company's reputation.
What I would like is to find a free (well, or for a reasonable amount) anti-spam filter through which you can drive the entire flow of letters with the ability to view content, flexible settings, view rejected letters and easy integration with microsoft exchange.

Answer 1

Method 3:
1. Buy a cloud service like Symantec.Cloud mastadon or something smaller, cheaper, but no less effective (this is your job - to find one)
2. Buy local software - a few years ago ORF left a good impression - domestic developer
3. Buy VPS on *nix, set up postfix + dnslbl + SpamAssassin there
The third way is the cheapest. But it requires qualification.
PS
Oh yes. None of the methods guarantee 100% protection against spam and false positives. There is a constant struggle until the mail protocol changes.