add automatic greylisting

bot/settings_bot.go

@@ -18,6 +18,7 @@ const (
 	botOptionQueueBatch     = "queue:batch"
 	botOptionQueueRetries   = "queue:retries"
 	botOptionBanlistEnabled = "banlist:enabled"
+	botOptionGreylist       = "greylist"
 )
 
 type botSettings map[string]string
@@ -56,6 +57,11 @@ func (s botSettings) BanlistEnabled() bool {
 	return utils.Bool(s.Get(botOptionBanlistEnabled))
 }
 
+// Greylist option (duration in minutes)
+func (s botSettings) Greylist() int {
+	return utils.Int(s.Get(botOptionGreylist))
+}
+
 // DKIMSignature (DNS TXT record)
 func (s botSettings) DKIMSignature() string {
 	return s.Get(botOptionDKIMSignature)