Hey, by all means go ahead - my personal reasons for doing it this way;

- Self contained dependencies managed for me by the maintainer of the image.

- I already run docker and keep all my configuration in a git folder that is structured in a way my brain works

- I already run watchtower which updates container for me automatically

- Other containers can use this container to send mail

- sendmail.cf scares me.

- filesystem isolation if it gets pwned