What services for online spam filtering do you know?

Question

Email

Good afternoon.
Share who knows what spam filtering services.
I mean services where you register their mx records in your domain and after filtering they send you letters. For example, the Spamorez service.
PS
Can someone explain how these services work? As far as I understand, all mail first goes to them, then they filter it and then somehow sort it into boxes already on your server. Here is the last step of interest. How does this happen?

Answer 1

It puts your mail server into boxes, to which mail is sent from similar "front-ends".
General scheme:
Sender's server -> Your edge, "front-end", aka cloud server -> Your mail server (for example, Exchange).
This is the middle link - it does basic checks, cuts off unnecessary load from your local servers (although it can also be local). There are many cloud services, ranging from Symantec.Cloud (I don't like their cloud service) to a dedicated and maintained by you VPS on Linux + postfix.