Sending and receiving email is important. When you register a domain name, you "buy" the right to create any email address on this domain (example: yourname@example.com if you have registered the domain name "example.com"). You must ensure that the domain's MX records are those of Gandi:
@ 10800 IN MX 10 spool.mail.gandi.net.
@ 10800 IN MX 50 fb.mail.gandi.net.
You need a server to host your mailboxes, just as you need a server to host your website.
Gandi offers an email service that is available to all our customers who register a domain name with us:
https://www.gandi.net/en/domain/email
You can create these mailboxes from your Gandi account, and we will make the changes to your DNS records automatically (provided your domain uses LiveDNS). You can also purchase additional email addresses, or increase the size of your existing mailboxes:
https://docs.gandi.net/en/gandimail/common_operations/create_email_address.html
To send and receive emails, you need an "email client". Most computers, tablets and smartphones come with an email client by default, but you can download your favourite software:
https://docs.gandi.net/en/gandimail/standard_email_settings/index.html