Which SMTP service port does a mail client usually connect to?
Is it the same for both SSL and Non-SSL?
Are there any common alternative?
The SMTP service uses port 25 by default. Secure SMTP (SSMTP uses SSL) uses port 465 by default. Although these are the defaults, pretty much every unused port number can be used. Most email clients will only try to connect to these ports unless instructed otherwise.
These are the default email service ports: