Once you have PowerMTA installed, you need to create SMTP user. To create an SMTP user, edit file
vi /etc/pmta/config
Find
# # password "changeme" #
Add below
password "SMTP_PASSWORD_HERE" source {smtpuser-auth} smtp-service yes always-allow-relaying yes require-auth true process-x-virtual-mta yes default-virtual-mta vmta-1 remove-received-headers true #add-received-headers false hide-message-source true #smtp-source-host 79.137.44.176 smtp1.serverok.in #domain-key default,smtp1.serverok.in,/etc/pmta/default.smtp1.serverok.in.pem max-msg-rate 100/h
In above code, replace SMTP_USERNAME_HERE and SMTP_PASSWORD_HERE with SMTP username and password you need.
in vmta-1, domain-key line that is commented out is used to Enable DKIM signing of out going emails.
Resatrt PowerMTA
systemctl restart pmta