Making grammatical mistakes in your email subject lines correlates with fewer responses to your emails, suggests an analysis by the email management tool Boomerang.
The company used an automated grammar-checking software to spot errors in 250,000 emails and tracked those emails’ response rates. Mistake-free subject lines received a response 34% of the time, compared to 29% of the time for emails with one or more errors. The more errors an email subject line had, the less likely the email’s recipient was to respond.
Not all mistakes had the same impact. The mistake most punished by non-response was not capitalizing the first letter in a subject line sentence. Emails with this flaw only received a response 28.4% of the time, compared to a 32.6% response rate for email subjects with correct capitalization—an approximate 13% drop in overall response rate.