The council's National Email Benchmarking Report also found that the number of marketing emails by all sectors has overtaken direct mail for the first time and increased by 50 per cent in the past quarter.
UK email service providers say that the volume of marketing emails across all sectors will grow by about a third on average over the next 12 months.
Megan Pacey, director of policy and campaigns at the Institute of Fundraising, said: "Emails are cost-effective for fundraisers, environmentally effective and targeted. But this is not the death of traditional direct marketing. Some audiences will always prefer to receive their information in different ways."