I want to set SMTP setting in outgoing email in CA but that SMTP is working on port 443. Will it work? I read one article which said that SharePoint outgoing email only works on port 25 and you have to use a relay in between that will take emails and forwards them to the SMTP running on port 443. Is this correct?
Outgoing mail is sent via port 25 - which is the default port for all SMTP traffic. You need to configure which "service/server" that will receive the message and then route it. Central Admin may be published on port 443 - but that is not the port being used for outgoing SMTP.
If you internal and have Exchange or another mail server that is usually the server you will point to. You may have configure SharePoint as a trusted sender, or create a transport rule to accept anonymous messages from it (it wont' work is the server requires authenticated sending).
If you don't have a mail server already - then you will need to configure an SMTP server. This can be done by installing the SMTP service on the SharePoint server or another machine.
If you need messages to be routed thru a public service like GMAIL, then your mail server or SMTP server will act as a relay. SharePoint can't authenticate to an SMTP server - but your relay server should be able too.
Yes, that is true till SharePoint 2013, SharePoint always use the default port 25 for SMTP.
But with New SharePoint version( 2016 preview), MSFT introduced an option, where you can change the SMTP port to non default.
you can read about this feature over here