Responsys director of strategic services EMEA Jon Stanesby said that the subject line is crucially important, so shouldn’t be seen as something that can be altered at the last minute.

If anything, the subject line should come first and then other elements should follow. More people see the subject line than any other element of the email campaign, so it’s absolutely vital to impress here.

But to make things easier, I’ve trawled the internet and come up with 10 things that should be avoided to ensure you don’t inadvertently harm your KPIs.

Obviously none of these rules are written in stone and it’s really up to marketers to test their own campaigns to find out what does and doesn’t work for their own customers, however this list does at least identify a few criteria to begin testing.

And for more information on this topic, check out our blog post detailing six case studies and an infographic on how to write effective email subject lines.

But, here are the 10 things that should be avoided…


In a recent Econsultancy survey 94% of businesses stated that personalisation is critical to their current and future success.

However too much personalisation in email, such as using the recipient’s name in the subject line, can have a detrimental effect according to Stanesby.

Brands should also be wary of being too personal in subject lines because this can seem overly familiar. Personalising subject lines too frequently also diminishes the effect and is best avoided.

Overt requests for donations

Heartwarming research by MailChimp found that subject lines that make a request for charitable donations have a negative impact on open rates.

However choosing the correct wording can at least mitigate the apparently repellent effect of asking people to send money for a worthy cause.

The word ‘donate’ was found to have the most negative impact, while ‘helping’ and ‘fundraising’ were the least damaging. However the latter two words can of course be used in a wider variety of contexts.

‘Last Chance’

In the aforementioned MailChimp study the phrase ‘Last Chance’ was found to have a hugely negative impact on open rates.

Obviously people don’t like to be reminded that they’re missing out on something they’ve already been emailed about.


Nothing says spam quite like a shouty, capped up subject line. It makes it difficult to read and is unlikely to have the desired effect of grabbing the reader’s attention.

As you can see in this example from my own spam folder, nothing says “I’m dodgy” quite like a capped up subject line offering a ‘LEGIT LOAN @ 3%’.

Sadly it seems that Gmail also feels that Apple and Advertising Week Europe are worthy of the spam bin…

The words ‘confirm’, ‘join’ or ‘assistance’

A study by Baydin identified seven words that were unlikely to provoke a response from recipients. They were confirm, join, assistance, speaker, press, social, and invite.

Vague or uninteresting subjects

A case study by communications blog AWeber found that clarity is an important factor for boosting open rates.

It compared clear, concise subject lines versus more creative versions in a test that ran across 20 subject lines and was sent to more than 45,000 subscribers.

The results are not that surprising as the creative examples were often vague or uninteresting, so did little to grab the reader’s attention.

Across each channel the clear, descriptive subject lines far outperformed the creative versions:

Too many characters

Stanesby said that though the rules change between different industries, generally firms should avoid long subject lines.

20 to 30 characters is plenty because consumers won’t read past that and most of the wording will likely be cut off on the screen, particularly on mobile devices.

Indeed the effect is magnified on smartphones due to the small screen size, and with upwards of 40% of emails now being opened on mobile devices it’s an issue that marketers can’t ignore.

It’s not possible to narrow it down to a specific length as there are other factors that play a bigger role in driving high open rates, however data from Mailer Mailer indicates that the sweet spot is somewhere between four and 15 characters.

Exclamation marks!!!

It seems logical that including several exclamation marks in a subject line is going to put the recipient off as it has the look of spam.

However as yet I’ve failed to come across any research that proves this to be the case.

In fact a cursory glance at my inbox shows that brands are more than happy to use exclamation marks, as well as caps and the word ‘free’, which is often cited as a blacklisted term that is sure to trigger spam filters.

Even so, I’m going to stick my neck out and say that using more than one exclamation mark looks spammy and should be avoided.


A study by Adestra found that consumers are too smart to be fooled when marketers add in ‘FW:’ or ‘RE:’ to the subject line to give the appearance of familiarity.

In fact the respective click rates were 47.5% and 42.6% lower than average. So don’t try to outsmart your customers as it’s underhand and they’ll likely see through it.

Bad content marketing, or marketing bad content

The same previously mentioned Adestra study found that certain forms of content marketing can actually harm open rates.

For example, using the word ‘report’ saw opens drop by 23.7% while CTR fell by 54.8%. The same is true for ‘webinar’ with the stats dropping by 16.6% and 70.7% respectively.

Conversely if the content is good, people will consume it. So ‘news’ (+34.8%, +47.7%), ‘bulletin’ (+15.8%, +12.7%) and ‘video’ (+18.5%, +64.8%) work well.