Use port 465 post email

[win]

container mailu-smtp-1 modify /etc/postfix/main.cf file, as follows：
smtp_tls_security_level=encrypt
smtp_tls_wrappermode=yes

container mailu-smtp-1 use the tool iptables to forward port 25 to 465
iptables -t nat -A OUTPUT -p tcp -s 192.168.xxx.xxx --dport 25 -j DNAT --to-destination :465
iptables -t nat -A INPUT -p tcp -d 192.168.xxx.xxx --sport 465 -j SNAT --to-source :25

192.168.xxx.xxx is the container mailu-smtp-1 IP address, also be possible not to set it up.

Test sending mail to server
Success：

1. 163(163.com)

Fail：

1. QQ(qq.com)
2. 189(189.cn)
3. aliyun(aliyun.com)
4. gmail(gmail.com)

Too many mail servers do not support 465. Sadness...

[Florent Daigniere]

The RFC is clear, listening on port 25 is what email servers ought to do.

see https://datatracker.ietf.org/doc/html/rfc5321#section-4.5.4.2