My mail server deliberately won't complete in under a second. This is because many spam systems don't actually speak SMTP - they just spew the protocol at you

My mail server deliberately won't complete in under a second. This is because many spam systems don't actually speak SMTP - they just spew the protocol at you and ignore what is being sent back. A little delay helps catch them. (In Postfix use sleep and reject_unauth_pipelining.)