The problem was cited by 44% of marketers who responded to the third annual Email Census by Econsultancy and Adestra, up from 32% last year.
In addition 69% of email marketing agency respondents said this was a major barrier for their clients, up from 53% last year.
Linus Gregoriadis, research director at Econsultancy, said: "While some companies are mastering various tactical elements of email best practice, such as segmentation, deliverability, list cleansing and triggered emails, it is clear that there are still problems for many organisations at a strategic level.
"A well-thought email strategy has to be the starting point for email marketing success."
The survey showed the appeal of email marketing has improved since last year, with 78% of company respondents rating the channel's return on investment as "excellent" or "good".
This is up from 66% from a year ago and makes email the highest rated digital channel for return on investment.