[ADD] maintain: setup mailjet api

closes odoo/documentation#3178

Signed-off-by: Antoine Vandevenne (anv) <anv@odoo.com>

content/applications/general/email_communication/email_domain.rst

@@ -167,6 +167,8 @@ To fully test the configuration, use the `Mail-Tester <https://www.mail-tester.c
 gives a full overview of the content and configuration in one sent email. Mail-Tester can also be
 used for other, lesser-known providers.
 
+.. _email_domain/default:
+
 Use a default email address
 ===========================
 

content/applications/general/email_communication/email_servers.rst

@@ -78,6 +78,8 @@ A G Suite server can be used for any Odoo hosting type. To do so, set up the SMT
 The configuration steps are explained in `Google documentation <https://support.google.com
 /a/answer/2956491?hl=en>`__.
 
+.. _email_servers/restriction:
+
 Restriction
 -----------
 
@@ -187,6 +189,8 @@ By default, inbound messages are fetched every 5 minutes in Odoo on-premise.
    :menuselection:`Settings --> Technical --> Automation --> Scheduled Actions` and look for
    :guilabel:`Mail: Fetchmail Service`.
 
+.. _email_servers/outgoing-email-server:
+
 Utilizing the From Filter on an outgoing email server
 =====================================================