Hello
Since june 2016, MailPress has been
withdrawn from the WordPress plugin repository due to an exploit
To be compatible with PHP 7, and to meet security requirements from the
WordPress Plugin Review Team,
I started to modify the plugin and posted a release candidate in April 2017 but it appears that this version is bugged (i am using PHP 7.2.3)
WordPress 5.0 is a big release and some of the technical options of old MailPress versions are no longer supported, so backward compatibility may not be possible.
PHP just released PHP 7.3.0 !
Some much work to do, so little time (and no financial support ;-( )
Happy holidays