Consumers will tolerate up to ‘about five emails’ per week from a given sender. Beyond that, ensuing complaints increase dramatically, and read rates drop significantly.

The findings form part of a report by Return Path, analysing the behaviour of over 600,000 web users over a three-month period in order to determine the ‘magic number’ of emails a recipient can receive from the same company in a given timeframe.

Analysing the sending frequency and engagement shifts from eight retailers where there was subscriber overlap, the report found a non-linear relationship between increased send frequency and increased complaints, finding five emails to be the optimum number of messages sent to engaged, primary users.

It’s long been common knowledge that consumers don’t respond well to spamming, with notes from the report warning of complaints, list churn, and deliverability issues as a result.

Send too little, however, and marketers are at risk of missing out on sales opportunities and “leaving money on the table”.

Perhaps counterintuitively, this could lead to a higher complaint rate, with each negative action making a bigger impact on a lesser total of sends.

Zero-inbox users

The report also unearthed surprising results when it came to engagement levels, with ‘zero-inbox’ users, or those that will make sure the majority of their messages get read, delivering 50% of complaints.

The findings cast doubt over practices of sending a higher frequency of messages to the most engaged users.

While only a quarter of the 67% bulk of ‘secondary’ recipients will open a marketing email, the study suggests that caution should be taken when making changes with a company’s valuable ‘primary’ echelon – constituting 83% of total opens – with the correct data and plenty of testing.

The report stated that while the read rate might be a bit lower, secondary accounts are a good test bed for trialing campaigns on a target audience.