I tried Test Mail Server Tool and while it worked great, you still need to open the email on some client.
I found Papercut: https://papercut.codeplex.com/
For configuration it's easy as Test Mail Server Tool (pratically zero-conf), and it also serves as an email client, with views for the Message (great for HTML emails), Headers, Body (to inspect the HTML) and Raw (full unparsed email).
It also has a Sections view, to split up the different media types found in the email.
It has a super clean and friendly UI, a good log viewer and gives you notifications when you receive an email.
I find it perfect, so I just wanted to give my 2c and maybe help someone.