Speaking only for myself, I have personally hosted my vanity domains that I have owned since 1995 with the folks at Heller Information Systems, who own the his.com and hers.com domains.
During that time, I was also the Sr. Internet Mail Administrator at AOL, and the co-author of the SAGE booklet on “Internet Postmaster: Duties and Responsibilities”. I know how hard it is to run an e-mail system properly, and how large of a team it takes to do the job right. And I have steadfastly refused to try to do that job on my own for myself. The folks at HIS do a better job than I could do on my own for myself.
Since 2003, I have also helped run the mail systems for python.org and NTP.org. That work has just solidified my views that running a mail server is a highly complex and burdensome task, which is why I drafted in the authors of “The Book of Postfix” to help run the mail systems for python.org. They have done a fantastic job, far better than I could have done on my own, and reinforced once again in my mind how much effort is required.
So, do your homework. Check out the long-term reputation of the company, and see how much of that might be due to a single person who is heroically trying to balance the entire world on their shoulders, versus those who are part of a large team.