There has been a lot of discussion in various places recently about subject line length and how it affects email marketing. There have been multiple studies done on how the subject line affects opens and clicks. (Mailchimp, Alchemy Worx, Mailer Mailer, Adestra). The discussion has even spilled over into Ken Magill’s newsletter today.
I’ve had a couple people ask me my opinion on subject line over the years. My general response is that subject line length is not directly measured by spamfilters and so don’t fret about the length. It is true that consistently crafting poor subject lines can indirectly cause delivery problems. Send mail few people open and that will hurt your reputation over time.
I think Ken really said it best, though.

It isn’t the length that sells. It’s the words.

The subject line should be long enough to tell the recipient why they should open your mail.
The subject line should be short enough that there is some information the recipient has to get in the mail.
The subject line should accurately reflect the offer inside
The subject line can contain words like “FREE” and exclamation points.
The subject line shouldn’t contain so many exclamation points that the recipient decides the mail is spam and doesn’t open it.
The subject line should be short enough the recipient can read it in their mail client.
A great subject line can lift opens and clicks, but fussing about the exact length of the subject line is probably an overall waste of time.

clicks • open rate • opens • subject • subject lines