I think pretty good one is security. If you are running your own mail server on your own domain, you need to figure out how to secure the domain and DNS against

I think pretty good one is security. If you are running your own mail server on your own domain, you need to figure out how to secure the domain and DNS against hijacking. Google provides some practical security here. It is well known that there's no human support available for Gmail, which means there's no support people who could be fooled by Mallory's social engineering skills. And of course if you took a bit wider view to the security, it includes also being able to access the data. While Gmail has probably had some issues in the past, I still feel it is more reliable than the internet connection which I have at home. This becomes a factor especially when I need to access my emails while travelling (and there's nobody at home sorting out possible connection problems).