“Some phrases affect response rates very positively. Take, for example, ‘Brand new’, ‘Latest’, and ‘Exciting’, which give open rate lifts of 37%, 24% and 19%, respectively…But some, well, aren’t so great. For example, ‘The perfect gift’, which imperfectly depresses open rates by -28%.”
Superlatives are words (adjectives or adverbs) used to describe something of the highest quality or degree. Words like awesome, perfect and excellent probably sound great in your head, but when used in the subject line of an email, they tend to fall flat.