Explaining to my sister how to set her iPhone, or to my brother and his wife who want to access the same email account on two computers... iPhone supports IMAP

Explaining to my sister how to set her iPhone, or to my brother and his wife who want to access the same email account on two computers... iPhone supports IMAP just fine, so that is not much effort :). But your point is true, operating a mailserver with reliable delivery is difficult, given the importance IP reputation. Badly maintained family boxes would just be a spam-nest. Also, for the $40 per year I spend on Fastmail, it is not really profitable for me. Though I had a mail server for a while, when it was still fun ;).