Such lists often contain invalid addresses.

This operation check detects errors in programming that cause invalid addresses.

On a 10K core array, invalid addresses are detected by the address-bus validity check.

Invalid Free - Passing an invalid address to free can corrupt the heap.

When a message is sent to an invalid address, it is "bounced" back to the machine that sent it.

The presence of invalid addresses in the list results in bounce messages being sent to the owner of the list.

If the mailing list is small, the owner can read the bounce messages and manually remove the invalid addresses from the list.

MS Exchange can tarpit senders who send to an invalid address.

Every time the spam arrives at an invalid address, it is returned to me - more than 750 times so far.

Dmalloc can find memory leaks, off-by-one errors, and usage of invalid addresses in some library functions calls.