If you get the following error in your /var/log/exim/mainlog when trying to send out welcome emails:
diradmin@host.name.com R=localuser T=local_delivery defer (13): Permission denied: cannot create /home/diradmin/Maildir/
that will mean that the receiving mail server is doing a sender check (or bouncing the email). Â You can satisfy this check by adding:diradmin: :blackhole:
to your /etc/aliases file so that the exim accepts emails to "diradmin" (but will just dump them into the abyss we call the blackhole). Â If you actually want to get the emails to diradmin, then change :blackhole: to be a valid email address, eg:diradmin: your@email.com
in the /etc/aliases file.