Can share what is the main benefits for own email server?

If you looking for cheap email hosting:
Actually now the email server is very cheap, especially under the shared hosting plan. With less than USD5 per month, you can have an unlimited email account if you know how to set it up properly.

If you looking for stable email hosting:
office 365, google workspace.

If you looking somewhere in between cost and stability:
exabytes, thegigabits.

One of the best email filtering service I know is Avanan, but it required you to have either google workspace email service or office 365 email service. Other standard email service provider do comes with spam filtering service.

Spam filtering is very important to save employees times, but most important is to have endpoint protection to detect and block email attachment that comes with virus/ransomware which can destroy your whole network.

I see, thanks for your information. I have no experience with government sector which might contain highly sensitive information. It should be worth to maintain own server for your case.

How about implement well know firewall email security gateway such as Sophos/Fortinet? What is the solution you are using now?