fix(email): test saved SMTP config and add TLS modes (#3388)

deploy/self-hosting/.env.example

@@ -318,7 +318,13 @@ FLUXER_EMAIL_SMTP_HOST=
 FLUXER_EMAIL_SMTP_PORT=587
 FLUXER_EMAIL_SMTP_USERNAME=
 FLUXER_EMAIL_SMTP_PASSWORD=
-FLUXER_EMAIL_SMTP_SECURE=true
+# How the SMTP connection is encrypted: implicit, starttls, opportunistic or
+# none. Leave it empty for implicit TLS on port 465 and required STARTTLS on any
+# other port.
+FLUXER_EMAIL_SMTP_TLS_MODE=
+# The older switch, read only while the mode above is empty. true is implicit
+# and false is opportunistic.
+#FLUXER_EMAIL_SMTP_SECURE=false
 #FLUXER_EMAIL_WEBHOOK_SECRET=
 
 FLUXER_DISCOVERY_ENABLED=true