There are two modes to connect to a Zimbra server, Regular mode and Admin User mode.
In regular user mode, we need access to SOAP web services, which are typically the following:
on port 80 if it is an HTTP connection;
on port 443 if an HTTPS connection.
In admin user mode, we also need access to SOAP web services, typically:
On port 80 and 7071 if the Zimbra URL is HTTP;
On port 443 and 7071 if the Zimbra URL is HTTPS.
You need to connect using both ports; some operations will go over the admin port, while others will go over the regular port.
Note: For step-by-step migration instructions, refer to the migration guide specific to your scenario. The guides, with Zimbra as a Source, can be found on our Community site, under Migration Guides/Mailbox Migrations.