greylisting is not the same.
greylisting is responding with a temp error under the assumption that most spam won't retry on temp errors, which isn't the case for most spam anymore.
real bounces are permanent errors.
greylisting is responding with a temp error under the assumption that most spam won't retry on temp errors, which isn't the case for most spam anymore.
real bounces are permanent errors.
As you say these days spammers will retry, but its an approach that still has value, because in the period between the initial delivery-attempt (which is rejected) and the final one (where it would be attempted) it is more likely that the sender has already appeared on DNS-based blocklists.