Every time I think about hosting my own mail server, I think back to the many, many, many times I’ve had to troubleshoot corporate email systems over the years. From small ones that ran on duct tape and prayers to big ones that were robust, high dollar systems.
98% of the time, the reason the messages aren’t coming or going is something either really obscure or really stupid. Email itself isn’t that complicated and it’s a legacy communications medium at this point. But it’s had so much stuff piled on top of it for spam and fraud prevention, out of necessity, and that’s where the major headaches come from. Honestly, it’s one service that to me it’s worth paying someone else to deal with.
I use a combination of both. SSD’s to store read/write intensive data. In my case, I run multiple VM’s and store the primary VHD’s on SSD’s. HDD’s for stuff where space matters more than speed, like digital media and local backups.