I'll counter the other comments. It's not any more difficult to maintain than any other service. What is a pain is the spam, and as I run it for a business the users. The biggest problem I have is other mail servers been incorrectly configured for SPF, DKIM and dmarc , usually it's things like external billing platforms that have been integrated incorrectly by customers and suppliers. Spam is now starting to come though with all the proper headers for SPF and DKIM