The Gandi offer includes free e-mail account for every domain you manage through Gandi, as well as a paying option (Mail Pack) which offers more storage space, email addresses, and an autoreply option.
You'll need to ask your primary DNS provider (usually your web host) to change the zone for this primary server. That is to say, edit the MX record according to your zone:
@ 10800 IN MX 10 spool.mail.gandi.net. @ 10800 IN MX 50 fb.mail.gandi.net.
You can then check your mails via mail.gandi.net and configure your e-mail client with help from our tutorials.
If you wish to use your usual e-mail client with the appropriate values for your domain (which isn't necessary, or useful, in 90% of cases), you'll need to add the following records at your web host:
pop 10800 IN CNAME access.mail.gandi.net. imap 10800 IN CNAME access.mail.gandi.net. smtp 10800 IN CNAME relay.mail.gandi.net. webmail 10800 IN CNAME agent.mail.gandi.net.