I got the following errors when setting up SMTP for the very first website on a brand new Ubuntu 20.04 LTS Linode VPS.
However it seems to be "just" a cosmetic issue because, as far as I can tell, the mail forwarding via SES seems to be working fine.
At least it does for the first site on this VPS.
**********************************
********** SMTP Setup **********
**********************************
* We only support TLS and Port 587.
+ SMTP Host: email-smtp.eu-west-2.amazonaws.com
+ User: B4LnfsH9fYo6uStL7+ikWcW
+ Password: BEUqpEREioYSqZnZKOh+YAKIA4K45gIN6376OV734
+ Main Hostname/Domain: domain.tld
postmap: warning: /etc/postfix/main.cf, line 46: overriding earlier entry: smtp_tls_security_level=may
postmap: warning: /etc/postfix/main.cf, line 32: overriding earlier entry: smtp_tls_security_level=encrypt
postmap: warning: /etc/postfix/main.cf, line 46: overriding earlier entry: smtp_tls_security_level=may
postmap: warning: /etc/postfix/main.cf, line 32: overriding earlier entry: smtp_tls_security_level=encrypt
postmap: warning: /etc/postfix/main.cf, line 46: overriding earlier entry: smtp_tls_security_level=may
postmap: warning: /etc/postfix/main.cf, line 32: overriding earlier entry: smtp_tls_security_level=encrypt
postmap: warning: /etc/postfix/main.cf, line 46: overriding earlier entry: smtp_tls_security_level=may
postmap: warning: /etc/postfix/main.cf, line 32: overriding earlier entry: smtp_tls_security_level=encrypt
postmap: warning: /etc/postfix/main.cf, line 46: overriding earlier entry: smtp_tls_security_level=may
postmap: warning: /etc/postfix/main.cf, line 32: overriding earlier entry: smtp_tls_security_level=encrypt
postmap: warning: /etc/postfix/main.cf, line 46: overriding earlier entry: smtp_tls_security_level=may
postmap: warning: /etc/postfix/main.cf, line 32: overriding earlier entry: smtp_tls_security_level=encrypt
postmap: warning: /etc/postfix/main.cf, line 46: overriding earlier entry: smtp_tls_security_level=may
SMTP was successfully enabled!
root@localhost:~#