Check port 25 and use smtp protocol to check postfix certificate. Fixes #3636 (#3637)

helper-scripts/expiry-dates.sh

@@ -3,7 +3,7 @@
 [[ -f mailcow.conf ]] && source mailcow.conf
 [[ -f ../mailcow.conf ]] && source ../mailcow.conf
 
-POSTFIX=$(echo | openssl s_client -connect ${MAILCOW_HOSTNAME}:143 -starttls imap 2>/dev/null | openssl x509 -inform pem -noout -enddate | cut -d "=" -f 2)
+POSTFIX=$(echo | openssl s_client -connect ${MAILCOW_HOSTNAME}:25 -starttls smtp 2>/dev/null | openssl x509 -inform pem -noout -enddate | cut -d "=" -f 2)
 DOVECOT=$(echo | openssl s_client -connect ${MAILCOW_HOSTNAME}:143 -starttls imap 2>/dev/null | openssl x509 -inform pem -noout -enddate | cut -d "=" -f 2)
 NGINX=$(echo | openssl s_client -connect ${MAILCOW_HOSTNAME}:443 2>/dev/null | openssl x509 -inform pem -noout -enddate | cut -d "=" -f 2)
 echo TLS expiry dates: