Which mail gateway should I choose?

Question

Mail server

Actually the subject is higher. And in more detail. 20k emails per week. 25 domains.
You need an anti-virus check, all sorts of DKIM, DMARC, SPF, PTR checks.
The presence of a cloud sandbox, or the ability to connect your own sandbox.
White/grey/black lists.
An antivirus program other than Casper.
We look at IMSVA and Fortimail. Something else?

Answer 1

https://www.forcepoint.com/product/email-security

Answer 2

iredmail

Answer 3

Proxmox Mail Gateway
https://www.proxmox.com/en/proxmox-mail-gateway

Answer 4

These guys are very good, we have been using them for several years https://www.spamexperts.com/services/incoming-filtering

Answer 5

zimbra but need 8GB RAM