Grey-listing Active

We've now implemented grey-listing on all incoming SMTP servers. Grey-listing is a user-transparent anti-spam measure that involves initially rejecting incoming mail from unknown sending address / host combinations, with a temporary SMTP error, and accepting it when the sending host tries sending it again.

All real SMTP hosts will retry sending a mail if it is initially rejected with a temporary SMTP error, but spam bots often do not. So the grey-listing mechanism is a simple and effective way to completely block a lot of incoming spam, while leaving legitimate messages unaffected (other than a small initial delay in delivering mail the first time mail is received from an unknown sending host / address combination).

Grey-listing is enabled at the system level and doesn't need any user intervention or configuration.