Postfix
This article explains how to use Sendamatic as an outbound relay, or smarthost, for Postfix.
Create the credential files
Add the following line to /etc/postfix/sasl_passwd
Create the postfix hashmap
Secure the credential files
sudo chown root:root /etc/postfix/sasl_passwd /etc/postfix/sasl_passwd.db
sudo chmod 0600 /etc/postfix/sasl_passwd /etc/postfix/sasl_passwd.db
Configure Postfix
sudo postconf -e "relayhost = [in.smtp.sendamatic.net]:587" \
"smtp_sasl_auth_enable = yes" \
"smtp_sasl_security_options = noanonymous" \
"smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd" \
"smtp_use_tls = yes" \
"smtp_tls_security_level = secure" \
"smtp_tls_note_starttls_offer = yes"
CA certificates
Postfix needs to be able to verify the Sendamatic SSL certificate. The location of your CA root certificates depends on the distribution you're using.
# Debian / Ubuntu
sudo postconf -e "smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt"
# Redhat / CentOS
sudo postconf -e "smtp_tls_CAfile = /etc/ssl/certs/ca-bundle.crt"
Finally, reload the Postfix configuration