[PATCH v2] docs: git-send-email: difference between ssl and tls smtp-encryption

[sndanailov@wired4ever.net]

From: Sotir Danailov <sndanailov@wired4ever.net>

New explanation for the difference between these values.
It's hard to understand what they do based only on the names.
New description of used default ports.

Signed-off-by: Sotir Danailov <sndanailov@wired4ever.net>
---
Changes since v1: Expanded explanation, covering more terms.
Link to v1: https://public-inbox.org/git/20221010172859.13832-1-sndanailov@wired4ever.net/

 Documentation/git-send-email.txt | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/Documentation/git-send-email.txt b/Documentation/git-send-email.txt
index 3290043053..d64a46fa87 100644
--- a/Documentation/git-send-email.txt
+++ b/Documentation/git-send-email.txt
@@ -178,9 +178,18 @@ Sending
 	for `sendmail` in `/usr/sbin`, `/usr/lib` and $PATH.
 
 --smtp-encryption=<encryption>::
-	Specify the encryption to use, either 'ssl' or 'tls'.  Any other
-	value reverts to plain SMTP.  Default is the value of
-	`sendemail.smtpEncryption`.
+	Valid values are 'ssl' and 'tls'. Any other value reverts to plain
+	(unencrypted) SMTP, which defaults to port 25.
+	Despite the names, both values will use the same newer version of TLS,
+	but for historic reasons have these names. The difference between the
+	two values for Git is the following. 'ssl' refers to "implicit"
+	encryption (sometimes called SMTPS), that uses port 465 by default.
+	'tls' refers to "explicit" encryption (often known as STARTTLS),
+	that uses port 25 by default. Other ports might be used by the SMTP
+	server, which are not the default. Commonly found alternative port for
+	'tls' and unencrypted is 587. You need to check your provider's
+	documentation or your server configuration to make sure
+	for your own case. Default is the value of `sendemail.smtpEncryption`.
 
 --smtp-domain=<FQDN>::
 	Specifies the Fully Qualified Domain Name (FQDN) used in the
-- 
2.37.3