The firm has hired broker Canaccord Capital Europe to handle the deal, with co-founder and CEO Lionel Thain and commercial director Ivan Southall launching a profile-raising campaign later this month.
It is hoped that £5m will be raised through the IPO, which Thain has said will be invested in boosting the number of registrations.
He said: "At the moment, we have got on average 100,000 new registrations a month, we would like to double that and this enables us to do that."
He added that when the firm launched, the intention was always to develop the business through an IPO and brokers had convinced him that now was the right time.
In February this year, the firm, which has just over 100 staff, launched a telemarketing service to complement its email work.
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