Postfix and clamsmtp smtp_bind_address

In order to send emails through Postfix outside of localhost, I had to set the Postfix smtp_bind_address to the server's private IP. The setting was required for both an Ubuntu 17.04 and Centos7 server. Clamsmtp Postfix settings likewise had to be set to the smtp_bind_address, as 127.0.0.1 created 'transport unavailable' errors. The comments by Jeff Roberson were applicable as well. Ubuntu settings as follows: clamsmtp.conf was set with clamav as the user; and owner permissions were changed from clamsmtp to clamav for the following directories/files: ClamAddress: /var/run/clamav/clamd.ctl TempDirectory: /var/spool/clamsmtp PidFile: /var/run/clamsmtp/clamsmtpd.pid (I read elsewhere that ownership permissions could also be resolved by adding user clamsmtp to the clamav group.) Local Socket files had to match: clamsmtp.conf - ClamAddress: /var/run/clamav/clamd.ctl clamd.conf - LocalSocket /run/clamav/clamd.ctl /etc/clamsmtp.conf OutAddress: 10026 Listen: 0.0.0.0:10025 ClamAddress: /var/run/clamav/clamd.ctl TempDirectory: /var/spool/clamsmtp PidFile: /var/run/clamsmtp/clamsmtpd.pid (symlink in Ubuntu, PidFile could be changed to /run/clamsmtp/clamsmtpd.pid) User: clamav /etc/clamav/clamd.conf: LocalSocket /var/run/clamav/clamd.ctl (symlink in Ubuntu, LocalSocket could be changed to /run/clamsmtp/clamsmtpd.pid) FixStaleSocket true LocalSocketGroup clamav User clamav Postfix main.cf: (Network Setting with server's private IP) smtp_bind_address=xxx.xxx.x.xx (clamsmtp Settings with server's private IP) content_filter = scan:xxx.xxx.x.xx:10025 receive_override_options = no_address_mappings master.cf: (clamsmtp Settings with server's private IP) scan unix - - n - 16 smtp -o smtp_send_xforward_command=yes # For injecting mail back into postfix from the filter xxx.xxx.x.xx:10026 inet n - n - 16 smtpd -o content_filter= -o receive_override_options=no_unknown_recipient_checks,no_header_body_checks -o smtpd_helo_restrictions= -o smtpd_client_restrictions= -o smtpd_sender_restrictions= -o smtpd_recipient_restrictions=permit_mynetworks,reject -o mynetworks_style=host -o smtpd_authorized_xforward_hosts=127.0.0.0/8 Start or Restart postfix, clamav-daemon (clamd), clamsmtp as root: systemctl restart postfix clamav-daemon clamsmtp Check status, all should be Active: systemctl status postfix clamav-daemon clamsmtp