I can't access or configure my email inbox on my terminal

Gandi mailboxes can be accessed via:

• any email client via standard POP and IMAP protocols
• our Roundcube and Sogo webmails: https://webmail.gandi.net

Be aware that in all instances (POP/IMAP and webmail), the username for accessing your mailbox is the full address of the mailbox (e.g. user@example.com). Please note that this username must not be confused with the username that allows you to access your Gandi account.
The password to access your mailbox is the one you chose when you created your mailbox. Once again, it should not be confused with your Gandi account password. If you forget your mailbox password, please reset it by logging into your Gandi account.

Check Gandi's POP/IMAP parameters to configure your email client
Resetting a Gandi mailbox password
More about the Roundcube webmail
More about Sogo webmail