When you join an Organization, all of your networks are transferred to the Organization.
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What you can do is change the email address of your account to a different address. From the account page, select “Manage Account” then “Personal Info”. From there you can change the email address.
Note: This email address must not already have a ZeroTier Central account.
Many users prefer to use something like “billing” or “admin” @example.com for their organization owner email account and then invite alice@example.com and bob@example.com as network admins.