The policy is partly intended "to encourage people who cannot afford internet access to sign up" a Maori Party spokeswoman said.
Maori Party MP Rahui Katene said that subsidy would pay for one gigabyte of data usage per email address with a maximum of five email addresses per household.
Ms Smith-Purkis later said the one gigabyte per email address subsidy was an annual allowance.
Broadband customers are not typically charged per megabyte of data usage unless they exceed their monthly allowances. After that they are generally charged about $2 per gigabyte.
Based on that price, the maximum annual saving would be $10 per household.
"The details need to be worked out in conjunction with the internet service providers, who we plan to work with on this policy," said Ms Katene "But our rough estimate based on the number of New Zealand households is that it would cost around $15-$25 million in its first year."
Under its Digital Technology Policy the Maori Party also wants to expand employment opportunities for Maori in the information, computer and telecommunications technology sector through Maori broadband group Nga Pu Waea including Maori cadetships in the digital creative sector.
It also wants investment in te reo versions of digital publications.