Why do account activation links expire quickly in welcome emails?

Hi all,

With our account activation links for our store, we are finding that the unique activation links in the welcome emails are expiring within just a few days. This is a big issue for our customer database as not all welcome emails will go to an Inbox, often they end up in spam only to be discovered a few days, weeks, months later. Is this something that is a setting within the backend of the store?

Kind regards,

Beau