Postfix is popular, secure, flexible, well documented, and likely to be around in 10 years. The defaults are quite sane and it's battle tested on numerous larg

Postfix is popular, secure, flexible, well documented, and likely to be around in 10 years. The defaults are quite sane and it's battle tested on numerous large mail servers. For a simple domain you only have to edit a few lines that numerous tutorials cover. Combining it with dovecot (similarly well designed, secure, popular, battle tested etc) makes for a robust setup. Sure don't make the mistakes the OP made and allow relaying for the the entire internet. I can't imagine any sane tutorial has relaying enabled by default. I've never heard of hMailServer, but hard to imagine it would be worth while and I wouldn't want to bet on it being around in 5-10 years. If editing a few config files and changing a few lines scares you then don't run a mail server. Otherwise pick something popular, well tested, and robust. Sure postfix+dovecot isn't the only solution, but I wouldn't pick something small/obscure/new either.