You can trigger an autoresponder when someone clicks a link in an email campaign that was sent out previously. For example, say you sent out an email campaign offering customers a special discount to folks that clicked a link in your email. You might want to send out a follow-up campaign to the customers that opened that email a few days later to remind them. You could use the "click" trigger to accomplish this.
If you use the click trigger, you will need to select which links Direct Mail should monitor for clicks. Campaigns that have already been sent out aren't eligible, but campaigns that are scheduled to send out in the future, or draft campaigns are eligible. You can instruct Direct Mail to monitor all the links in a campaign, or just the ones you choose.
If a recipient unsubscribes or is removed from your mailing list before they click the triggering link, they will not be sent the autoresponder.