Most spammers take advantage of the default address settings of your account whereby the mail will still reach your account even if the address is wrong. This causes large Influx of spams and will take your valuable disk space.
There are 2 options for dealing with this
1. Setting default address as :blackhole: – This will let us first allow the mail to reach your server, accept it, validate it and throw it if it has a non-existent address. The drawback of this is it still consumes your server’s valuable bandwidth and processing time.
2. Setting default address as: fail: – This will stop the mails from entering the server in the first place and send a bounce message back to the sender. This method is more preferable as it saves the server’s resources and thus keeps it performing even under spam attacks.