> The email takes 10 seconds to show up. Even longer if you have greylisting turned on, it gets temporarily rejected which means you then have to wait N minute

> The email takes 10 seconds to show up. Even longer if you have greylisting turned on, it gets temporarily rejected which means you then have to wait N minutes before it gets accepted (assuming they retry sensibly and don't just spam retries every 2 minutes and get fail2ban'd.) By which time it might well have timed out anyway...