Spark is moving its Xtra email service to New Zealand-owned company SMX after the sale of Yahoo! to Verizon for $US5billion ($NZ6.8billion) in July.
Spark home, mobile and business chief executive Jason Paris said the decision to partner with Auckland's SMX was great news for customers.
''Our customers tell us their email service, including their @xtra.co.nz email address, is critically important to them. After a positive nine-year relationship with Yahoo! we have decided to transition our email service to SMX. We know email is a critically important service to our customers and we are dedicated to making this transition as seamless as possible for our users.''
Spark would seek customers' permission to move their data from today and would progressively move Xtra customers to the new email platform over a three-month period from January next year.
All customers would keep their existing Xtra email address.
SMX was founded in 2006 and is a New Zealand cloud email technology company.
Shareholders include Trade Me founder Sam Morgan and The Warehouse founder Sir Stephen Tindall. More than 60% of New Zealand government departments used SMX for their email security.
Spark last year moved more than 11,000 Spark business mailboxes to SMX, Mr Paris said.
In the United States, Yahoo! will be combined with AOL, another faded internet star, which Verizon bought last year.
The deal did not include Yahoo!'s valuable stake in Chinese firm Alibaba.
The price tag for the deal is well below the $US44billion Microsoft offered for Yahoo! in 2008 or the $US125billion it was worth during the dot-com boom.
Verizon said the deal for Yahoo's core internet business would make it a global mobile media company.
