Would need to check the code to see what we are doing but this is a useful reference document explaining the different protocols available and the common naming problem

https://www.fastmail.com/help/technical/ssltlsstarttls.html

Yes, that exacly the problem i described.

For instance having an SMTP mail server with:

• port 25: SMTP + StartTLS Extension) + Auth
• port 465: SMTPS + Auth
• port 587: SMTP + StartTLS Extension + Auth

And only supporting TLS 1.0+ protocols. No SSL protocol support.

When configuring joomla:

• port 25 or 587 works on Joomla "TLS" option, so i think is really SMTP+StartTLS (SMTP + StartTLS extension)
• port 465 works on Joomla "SSL" option, so i think is really SMTPS (SMTP over SSL/TLS)

For joomla user configuration pourposes the security protocol (SSL or TLS) implemented by the SMTP mail server is not relevant. Presuming every thing else is ok, if the user server supports the same security protocol and ciphers of the smtp mail server it will be ok.
For that pourpose, is more relevant if it uses SMTP or SMTP+StartTLS or SMTPS and in witch port.

More info:

• SMTP https://tools.ietf.org/html/rfc5321
• SMTP Start TLS https://tools.ietf.org/html/rfc3207

Also i think Joomla uses PHPMailer class with this code
See https://github.com/joomla/joomla-cms/blob/staging/libraries/joomla/mail/mail.php#L468

It also seems PHPMailer uses "ssl://" for SMTPS and no prefix for SMTP+StartTLS.
See https://github.com/joomla/joomla-cms/blob/staging/libraries/vendor/phpmailer/phpmailer/class.phpmailer.php#L1312
And the StartTLS part https://github.com/joomla/joomla-cms/blob/staging/libraries/vendor/phpmailer/phpmailer/class.phpmailer.php#L1334
and
https://github.com/joomla/joomla-cms/blob/staging/libraries/vendor/phpmailer/phpmailer/class.smtp.php#L315

Closed. PR