Well maybe I shouldn't be shocked, but I am still. Not at the security issue but looking at that MX server survey I had no idea that Exim and Postfix combined had that high of a market share, and that Sendmail was at 40% ~15 years ago and is now at under 4%. I really expected nobody to have more than say 20-25% market share. Personally I have been using Postfix since about 2001 I think. It was suggested to me for a anti virus solution I was looking to deploy at the time and just haven't had a need to look at anything else.
I went off to look at sendmail.org, and wow they are old school(except they seem to be operating under the "ProofPoint" brand not sure when that happened), just read the stuff under the "Contact us" section. Also it's the first reference to a FTP server I have seen on a website in a long time(I have nothing against ftp myself other than it is funky to work through firewalls).
I still prefer text email myself and my personal email server does strip html off of incoming emails automatically which can sometimes make things difficult (and in very rare occasions impossible as in the entire message is empty) to read. But it certainly brings back memories of an earlier era(an era that was much more fun for me computing wise anyway).
For work my org uses office 365 (and hosted exchange at rack space prior), MS introduced breaking changes in the OWA client which I use for most of my mail which makes text based email composing impossible. Reported it almost 2 years ago and last I checked it was still broken (the behavior being new line characters are broken making the entire email be one long line, in many cases totally unreadable. Message is fine in the "outbox" and only gets mangled once it gets beyond that level).