Spark will be moving its Xtra email service to New Zealand-owned email provider SMX.
Customers who use @xtra.co.nz email addresses need to give Spark permission to move their data to the new platform.
The transfer of Xtra customer data will take three months from January next year and customers can begin the process from today. Email addresses won't need to be changed.
SMX is based in Auckland and rich lister Sam Morgan is one of its major shareholders.
Spark Home, Mobile and Business CEO, Jason Paris said 11,000 Xtra business customers were moved to SMX last year.