You then will need to tell your web host the name of your domain so that they can configure their servers. Careful: there is no need to transfer your domain to them in order for this to work, you just need to let them know the name of your domain.

Then, you need to create the e-mail address that you want via their web interface; there is no need to contact Gandi to do this, because your web host will be in charge of handling your e-mail. Your web host will also tell you your POP/SMTP password and settings.

Once you have configured your e-mail at your web host, you need to change the DNS attributed to your domain name at Gandi. To do this, begin by logging into your domain's control panel with the owner, administrative, or technical Gandi handle (remember, if you have more than one domain, you need to click on the domain in your list of domains).

Then, look to the "Technical Settings" section towards the bottom of the page…

…and click on the "Manage DNS zone file" which is in the "Technical" column. This will bring up the DNS zone file management page. From there, choose the interface that you are most comfortable with ("simple", "normal", or "expert") and add a MX record (your web host will tell you this: it is the name of their mail server).