How do you clean up an old phone number list?

A list a few years old always contains numbers that no longer exist. You pay for those all the same, and the failures distort your figures.

What goes wrong in a list

People change numbers. Companies disappear. There are typos, landlines in a mobile field, and numbers without a country code. In hand-built lists, a tenth is typically unusable.

An HLR lookup

You ask the network whether a number is still active, without sending a message. You get back, per number, whether it exists, which network it belongs to and whether it was ever ported. That costs a fraction of a real send.

What you do afterwards

Delete what is dead rather than keeping it for later. Correct what is clearly a typo. And note when you cleaned up, so you repeat it periodically instead of once.

What it yields

Lower costs, but above all more reliable figures: your delivery rate then measures the quality of your message and not the age of your list.