Best practices for email marketing subject lines

Best practices for email marketing subject lines

Last month I received an email from a trusted sender with the subject line “Re: ideas in your inbox.” I was confused as to why I was receiving a reply to a message I did not write with a subject I did not know. When I opened this email, I discovered that it was not a reply email but that it was a marketing email with a misleading subject line. This was not a mistake or typo as I have continued to receive marketing emails from this company with “Re:” in the subject line over the last month.

email_marketingStudying open rates of marketing emails and performing A/B tests to see which subject lines generate the most opens is a practice that we highly encourage with all of our email marketing clients. However, it’s important to make sure you’re looking at what the metrics mean – not just the numbers.

The marketer that sent out the Re: emails likely looked at his open rates and noticed that they went up when he used this misleading subject line. Success, right? No. More people may have opened the email because they were tricked into thinking it was a response to something they sent; however, once his recipients realized they were tricked, I am sure the unsubscribes will go up and the feeling toward this company and ultimately their sales will go down. Sales and your brand reputation should always be the goal – not open rates or clicks. If you’re only focusing on moving those numbers then you are missing the point and potentially doing more damage than good.

We’ve seen in-house marketers who understand this, but who are responsible for simply moving those numbers and their performance is judged by execs who may be blindly looking at the numbers. In this case we would recommend standing up and pointing out this flaw in measuring success. In doing so you’ll be seen as an employee who sees the big picture and is focused on driving the strategy, not just an easily replaceable cog in the wheel.

To help you both improve those open rates and better focus on the bottom line we’ve put together a list of DO’S and DON’TS for email subject lines:

EMAIL SUBJECT LINES – DO’S

  • Test your subject lines. A/B test your subject lines to see which performs better. If your list has 3,000 people on it, send 500 people an email with subject A, and 500 people the same email with subject B. If one of them has more clicks, use that subject line when sending to the remaining 2,000 people on your list.
  • Not related to subject lines, but you can also test the From label. Test and see if people respond better to your company name as the sender or as an employee’s name. Results vary depending on the brand, industry and list – so test it!
  • Make your subject line relevant to the message. Seems like a no brainer, but we often see marketers try and get clever with some attention grabbing subject line that has nothing to do with the actual message. Like reply trick mentioned above.
  • Try framing subject lines as a question or with another call to action
  • Give the user an idea of what is in the email
  • Look at the quality of your list. Maybe it’s them and not you. How did they get on your list? Do they expect or want an email from you?
  • Consider the frequency of your emails and time sent. We get asked all the time what the best day and time to send an email is. The truth is – it depends on your list. The only real way is to test it. I can tell you that the first thing I do each morning is bulk delete spam and stuff I know I don’t need to read so I’d avoid being in that large batch of early morning deletes.

EMAIL SUBJECT LINES – DON’TS

    • DON’T WRITE IN ALL CAPS AND INCLUDE EXCLAMATION POINTS!!! Not only is this obnoxious, but you’re more likely to end up in a spam filter.
    • Don’t worry about number of characters. Don’t make it obnoxiously long and keep in mind that on certain devices and platforms users may only see the first 40-50 characters, but despite all the info about subject line length studies show that length doesn’t actually effect open rates.
    • Don’t use spammy words like FREE or open immediately
    • Don’t use symbols or strange characters
    • Don’t over sell in the subject line

When done correctly, email marketing is one of the most effective ways of engaging with your customers and prospects. At MODassic, we carefully study many campaign metrics and constantly make adjustments to refine an email marketing strategy and deliver ROI.

Download our Email Marketing Best Practice


  • Most of my customers open their emails on the iPhone. So I have to worry about the number of characters, because the iPhone greatly truncates the subject line.

    How come big companies like Walgreens, Best Buy, Apple, GoDaddy use spammy words like Free and they use $ and % signs? They also oversell in their subject lines, especially Walgreens and GoDaddy.

    I’m not sure to whom these general rules apply while big companies ignore them. Can you help?

    • modassic

      Hi Goran – thanks for the comment. They are definitely general guidelines not rules.

      Overselling in the subject line won’t necessarily get your email automatically flagged as spam, but we’ve found that overselling causes recipients to be more likely to manually mark your email as spam instead of just deleting it if they weren’t interested. The same goes for subject line length. A longer subject line won’t get you automatically flagged as spam and while they may not see your full subject line on the iphone it hasn’t shown to effect the open rate. My recommendation would be to just make sure the part they can see has is engaging enough for them to want to open it.

      Also, we have a client that we send 2 promotional emails a month for and the majority are for a free gift with purchase. With this client we have a very clean list so we’ve been able to use the word “free” in the subject line without any problems. We don’t put it in all caps, but do use it regularly in the subject line. The more important factor quality of your list. If it’s high quality, meaning they are expecting your email then as long as you are sending from a reputable IP address.

      • Thank you so much for a great response. Cheers.

  • modassic

    Hey Goran – thanks for the comment. They are definitely general guidelines not rules.

    Overselling in the subject line won’t necessarily get your email automatically flagged as spam, but we’ve found that overselling causes recipients to be more likely to manually mark your email as spam instead of just deleting it if they weren’t interested. The same goes for subject line length. A longer subject line won’t get you automatically flagged as spam and while they may not see your full subject line on the iphone it hasn’t shown to effect the open rate. My recommendation would be to just make sure the part they can see has is engaging enough for them to want to open it.

    Also, we have a client that we send 2 promotional emails a month for and the majority are for a free gift with purchase. With this client we have a very clean list so we’ve been able to use the word “free” in the subject line without any problems. We don’t put it in all caps, but do use it regularly in the subject line. The more important factor quality of your list. If it’s high quality, meaning they are expecting your email then as long as you are sending from a reputable IP address.

  • loras

    Last month I decided to try GetResponse software and now I have an opportunity to use your tips about creating good email marketing subject lines- thanks a lot!