fix: disable mailpit rdns to avoid smtp delays (#4440)

* Disable Mailpit Rdns To Fix Smtp Delays (#40343)

* Apply suggestions from code review

* Apply suggestion from @sweatybridge

---------

Co-authored-by: Han Qiao <sweatybridge@gmail.com>

Author: Adityakk9031

internal/start/start.go

@@ -763,6 +763,10 @@ EOF
 			ctx,
 			container.Config{
 				Image: utils.Config.Inbucket.Image,
+				Env: []string{
+					// Disable reverse DNS lookups in Mailpit to avoid slow/delayed DNS resolution
+					"MP_SMTP_DISABLE_RDNS=true",
+				},
 				Healthcheck: &container.HealthConfig{
 					Test:     []string{"CMD", "/mailpit", "readyz"},
 					Interval: 10 * time.Second,