Port 25 is the standard port that is used over the internet for SMTP communication. If you wish to talk to someone else then it will be over port 25.
You can use alternate ports internal to your own network; eg if you have an Amazon server you could configure it to use port 2525 and configure your local machine to talk to that port. But talking to anyone else (eg Google, as in your example) must be on port 25.
You may find your ISP has a relay server that you can use (maybe with authentication). This is typically how ISPs try to stop letting people spam out; if you can't talk to the internet on port 25 and must go through their relay then they can rate limit, spam filter, etc.
Another solution, if you have an external server (eg Amazon) would be to configure a VPN between your machines; that'll bypass the ISP port 25 restrictions.
http://blog.mailgun.com/25-465-587-what-port-should-i-use/
http://stackoverflow.com/questions/15796530/what-is-the-difference-between-ports-465-and-587
Ports 465 and 587 are intended for email client to email server communication (sending email).
Port 465 is for smtps
SSL encryption is started automatically before any SMTP level communication.
Port 587 is for msa
It is almost like standard SMTP port. MSA should accept email after authentication (e.g. after SMTP AUTH). It helps to stop outgoing spam when netmasters of DUL ranges can block outgoing connections to SMTP port (port 25).
SSL encryption may be started by STARTTLS command at SMTP level if server supports it and your ISP does not filter server's EHLO reply (reported 2014 Nov).
Port 25 is used by MTA to MTA communication (mail server to mail server). It may be used for client to server communication but it is not currently the most recommended. Standard SMTP port accepts email from other mail servers to its "internal" mailboxes without authentication.
You can use alternate ports internal to your own network; eg if you have an Amazon server you could configure it to use port 2525 and configure your local machine to talk to that port. But talking to anyone else (eg Google, as in your example) must be on port 25.
You may find your ISP has a relay server that you can use (maybe with authentication). This is typically how ISPs try to stop letting people spam out; if you can't talk to the internet on port 25 and must go through their relay then they can rate limit, spam filter, etc.
Another solution, if you have an external server (eg Amazon) would be to configure a VPN between your machines; that'll bypass the ISP port 25 restrictions.
http://blog.mailgun.com/25-465-587-what-port-should-i-use/
http://stackoverflow.com/questions/15796530/what-is-the-difference-between-ports-465-and-587
SMTP protocol: smtps (port 465) v. msa (port 587)
Ports 465 and 587 are intended for email client to email server communication (sending email).
Port 465 is for smtps
SSL encryption is started automatically before any SMTP level communication.
Port 587 is for msa
It is almost like standard SMTP port. MSA should accept email after authentication (e.g. after SMTP AUTH). It helps to stop outgoing spam when netmasters of DUL ranges can block outgoing connections to SMTP port (port 25).
SSL encryption may be started by STARTTLS command at SMTP level if server supports it and your ISP does not filter server's EHLO reply (reported 2014 Nov).
Port 25 is used by MTA to MTA communication (mail server to mail server). It may be used for client to server communication but it is not currently the most recommended. Standard SMTP port accepts email from other mail servers to its "internal" mailboxes without authentication.
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