smtp_generic_maps = hash:$config_directory/generic

$config_directory/generic:
	""	postmaster@example.com
	<>	postmaster@example.com

Actually not sure which one works...

I kindda know this whole stuff is written in completely wrong way, but I have
reasons for that. SaMoToP prevent me from creating a separate transport so I'm
just using MailDir and directly reading files from there in separate task. Also
socket permissions can't actually be hinted to SaMoToP, and I don't want to
mess with umask in this case, hence the extra task that changes socket
permissions later. The whole MailDir idea was shamelessly ripped from
https://github.com/meysam81/lori, kudos to the author. And if you think I
actually copypasted too much code - you are free to use this under APACHE-2.0
license.