What is your greatest frustration when sending email?

After surveying 3308 email users over the past 17 years, the #1 frustration people report is

‘Getting no response to your e-mail when you send a message that clearly requires a response (or response is too slow)’?

This is clearly the biggest of the 17 common frustrations listed in the survey. The Top 5 almost always feature whenever I run this survey and you can see the full list below: