config: validate mail configuration certificates by default (#388)

Before this commit, the default was to not validate TLS certificates of
the SMTP server. This is perhaps a rather unexpected default and can be
considered insecure. This commit activates mail server TLS cert validation
by default.

This change might break some users' email configuration, if they did not
explicitly set the `mail.cert_validation` config variable. Nonetheless,
I think that the secure option should be the default option (e.g.,
to prevent man-in-the-middle attacks and breaching mail server login
credentials).

Signed-off-by: klmmr <35450576+klmmr@users.noreply.github.com>

docs/documentation/configuration/overview.md

@@ -58,7 +58,7 @@ mail:
   host: 127.0.0.1
   port: 25
   encryption: none
-  cert_validation: false
+  cert_validation: true
   username: ""
   password: ""
   auth_type: plain
@@ -289,7 +289,7 @@ Options for configuring email notifications or sending peer configurations via e
 - **Description:** SMTP encryption type. Valid values: `none`, `tls`, `starttls`.
 
 ### `cert_validation`
-- **Default:** `false`
+- **Default:** `true`
 - **Description:** If `true`, validate the SMTP server certificate (relevant if `encryption` = `tls`).
 
 ### `username`

internal/config/config.go

@@ -145,7 +145,7 @@ func defaultConfig() *Config {
 		Host:           "127.0.0.1",
 		Port:           25,
 		Encryption:     MailEncryptionNone,
-		CertValidation: false,
+		CertValidation: true,
 		Username:       "",
 		Password:       "",
 		AuthType:       MailAuthPlain,