An autoresponder is an automatic email that is triggered by a specific event or action, such as a subscriber signing up for a mailing list. It is important to have an autoresponder because:

It allows you to automatically respond to common inquiries and tasks, such as confirming a subscription, providing information about a product or service, or delivering a digital asset.
It helps to nurture leads and build relationships with subscribers by providing valuable content and keeping your brand top-of-mind.
It increases the productivity of your customer service team by handling common requests automatically.
It helps in building trust and credibility with your audience by providing them with instant confirmation and valuable information.

When choosing an autoresponder, you should consider the following factors:

Integration: Make sure the autoresponder integrates with your website and other tools you use.
Automation: Look for a service that allows you to set up complex automation sequences.
Deliverability: Check the deliverability rates of the service to ensure that your emails are reaching the inbox.
Reporting and Analytics: Look for a service that provides detailed reporting and analytics to help you track the success of your campaigns.
Email Templates: Look for a service that offers a wide variety of email templates that are easy to customize.
Customer support: Look for a service that offers excellent customer support to help you with any issues you might encounter.

Some of the popular autoresponder services include Mailchimp, Constant Contact, Aweber, GetResponse and Drip.