Thanks Jim,
That corresponds with what I see in actual tests too.
/etc/postfix-msa/master.cf: smtpd_tls_security_level=none
pfSense E-Mail Notifications:
Port: 587, Enable STARTTLS: No, SMTP testing e-mail successfully sent
Port: 587, Enable STARTTLS: Yes, Could not send the message to xxxxx@xxxxx.com – Error: server does not support starting TLS
/etc/postfix-msa/master.cf: smtpd_tls_security_level=may
pfSense E-Mail Notifications:
Port: 587, Enable STARTTLS: No, SMTP testing e-mail successfully sent
Port: 587, Enable STARTTLS: Yes, SMTP testing e-mail successfully sent
/etc/postfix-msa/master.cf: smtpd_tls_security_level=encrypt
pfSense E-Mail Notifications:
Port: 587, Enable STARTTLS: No, Could not send the message to xxxxx@xxxxx.com -- Error: server does not require authentication, it probably requires starting TLS
Port: 587, Enable STARTTLS: Yes, SMTP testing e-mail successfully sent
This would seem to indicate that pfSense version 2.3.2 requires TLS, rather than falling back to plain text mode, when the E-Mail Notification option to "Enable STARTTLS" is selected.