Subject lines

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.

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When an open is not a sign of interest

A lot of people, including myself, are using opens as one of the measures of engagement. This, as a general rule, is not a bad measure. However, there are people who will open email not because they’re interested in it, but because they know it is spam.
Take, for instance, the email address I acquired in 1993. Yes, I still have this address. I stopped using it to sign up for lists in 1999 and stopped using it for most of the rest of my mail around 2001. This address, though, is on any number of spam mailing lists. The spam that gets through is usually sent by hard-core spammers. The ISP that hosts that mailbox uses Communigate Pro to filter mail, so much of the casual spam is filtered.
Generally, if I open an email (and load images or click through) on that account it is only in order to track down a spammer. For instance, I’m getting a lot of spam there from affiliates offering me the opportunity to purchase printing services for a very low price. I have actually been opening the mail, and clicking through. But I’m not clicking through because I’m interested in purchasing. I’m clicking through to see if my reports to abuse@ printer are resulting in any action against the spammers. (They’re not).
The thing is, though, I know that by clicking through on ads, I’ve now been promoted by the spammer to the “clicks on emails! it’s a live address!” list. Which only means I’m going to get more spam from them. Lucky me.
Using clicks and opens as a measure of engagement isn’t necessarily bad. But when using them you have to understand the limitations of the measurement and that what you may think it’s telling you isn’t actually what it’s telling you.

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Reporting email disposition

Most regular readers know I think open and click through rates are actually proxy measurements. That is they measure things that correlate with reading and interacting with an email and can be used to estimate how much an email is wanted by the recipients.
The holy grail is, of course, having ISPs report back exact metrics on what a user did with an email. Did the user read it? Did it stay open on their screen a long time? Did the user just mark it read or throw it away? What happened to the message. Marketers would love this information.
It’s unlikely the ISPs will ever provide this information to marketers. Take away all the technical challenges, and there are some significant ones there are still social challenges to making this data available. Current user contracts protect the privacy of the user, local laws prohibit sharing this data. And, there is the vocal group of privacy advocates that will protest and raise a big stink.
I’m not sure why email is gets the special treatment of expecting the channel owners to provide detailed disposition data. In no other direct marketing venue is that information collected or provided. TV stations can’t tell advertisers whether or not someone watched a commercial, fast forwarded through it or got up to grab a beer from the fridge. The post office can’t tell direct mail marketers whether or not a recipient read the mail or just dumped it in the big recycling bin the post office provides for unwanted messages. Billboard owners can’t tell advertisers how many people read the billboard.
Since we can’t get exact read rates from ISPs, what do we do? We look at proxy numbers.
Read rate directly measures who opened the message. Open rate is a proxy. It’s who displayed images in the message.
Read rate can be measured only by people who have access to the user’s inbox. The ISPs can measure read rate because they have full access to the mailbox, but this requires the user to access the mailbox through webmail or IMAP. Some third party mailbox addons can measure it, but this requires the cooperation of the mailbox owner. If the mailbox owner doesn’t install the reporting tool, then the 3rd party doesn’t have access to the data. Only groups with access to the end users mailbox can measure this rate.
Open rate can be measured by people who have access to the server images are hosted. Senders and ESPs and 3rd parties can measure it if they provide unique image IDs or tracking pixels in their emails. Open tracking does require the cooperation of the recipient – they have to have images on. No images on, no open tracking. Ironically, ISPs cannot measure open rate, because they have no access to the image hosting servers.
Click rate can be measured by people who have access to the server that hosts the website. The same people who can measure opens can measure clicks. Some ISPs can measure clicks, Hotmail used to pass every URL through a proxy they hosted and they could count clicks this way. AOL controls the client so they could measure number of clicks on a link. I’ve heard trustworthy folks claim that ISPs are measuring clicks and that they’re not measuring clicks (any of the Barry’s want to comment?).
Without controlling the inbox, though, senders have to rely on proxy measurements to judge the effectiveness of any particular campaign. But at least email marketers have proxies to use for measurement.

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What does open rate tell you

There has been an lot written about open rates in the past, but there are two posts that stand out to me. One was the EEC’s post on renaming open rate to render rate and Mark Brownlow’s excellent post on what open rate does and does not measure. I’ve also weighed in on the subject. The issue is still very confused.
If asked, most people will tell you that open rate is the number of emails that were opened by the recipient. The problem is that this isn’t actually true. Open rate is measured by the number of people that display an image in an email. Traditionally this has been a uniquely tagged 1×1 pixel, until some filters and mail clients stopped displaying 1×1 pixels. More recently, every image in an email is tagged, so opening one image would record as an open.
So open rate doesn’t actually tell a sender how many people opened and read an email. It really only records that an image in a particular email is loaded. It does not record when an email is opened. Some people don’t load images by default. Some people don’t load images at all, even when they open and actively read the text portion of the email.
Clearly, there are some uses for open rates. It can give a useful metric when comparing different forms of the same email (A/B testing) and when looking at user engagement over time. However, we have also recently seen that open rate is not predictive for click through rate.

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