One press director said the publisher is not releasing information on how many consumers open the email title, making it difficult to track return on investment.
Rivals also claim its database of 250,000 consumers registered to receive the email contains considerable duplication. 'People signed up to win a car, not just to receive a newsletter,' added one.
The title has also suffered from production problems; the last three pages of the current issue are off-centre.
James Carter, NPD director at Dennis Publishing, said: 'Monkey has signed up to the ABCs and will be delivering an audit of its figures to coincide with print title releases in February, as it continues to outperform its launch targets.'