7 Tips to Avoid Bursting Your Email Deliverability Balloon

The Email Deliverability balloon“If I do X” will my emails go to the junk folder is a question I’m often asked by clients. Questions such as “if I put free in the subject line”, “if I don’t use DKIM”, “if my email is all images”.

Email deliverability and spam filtering work like blowing up a balloon,  if you blow to hard it bursts, the email is spam. Many individual issues contribute a puff of air into the balloon.

Some, such as spam complaints, give a bigger puff of air than others. Once the amount of air reaches a critical point, the balloon bursts and the email goes to spam rather than the inbox.

Just as for a real balloon, no one particular puff is responsible for bursting the balloon and no single puff will cause the balloon to burst, it is the sum of all puffs that’s important.

Seven things that blow up your email deliverability balloon

The key items that cause a puff air into your balloon and poor email deliverability are, in order of importance:

  1. Data source and collection practice
  2. Poor bounce management
  3. Poor complaint feedback loop management
  4. Content issues
  5. Poor data management
  6. Infrequent emailing
  7. Lack of authentication (SPF, DKIM)


These are the issues that most likely cause inbox placement problems. The number one is data source and data collection practice. This is because how the recipient sees their relationship with you has a big impact on their behaviour – will they hit the spam button or read your email? Good data drives good user engagement, good user engagement drives great reputation and great reputation drives the best inbox placement.

The big inbox providers, including Gmail and Microsoft heavily look at engagement to determine your sender reputation and whether you should go to junk.

Whilst the exact details of how reputation is calculated are kept secret, the ISPs have publicly discussed the concepts they use to calculate reputation. A big part of which is behaviours.

Gmail looks at these behaviours as positives, reasons to keep putting your emails in the inbox

  • Reading. If your emails are read it suggests they were wanted
  • Reply. When a person replies to the sender it’s a very strong indicator they wanted the email. Encourage your subscribers to reply
  • Move out of junk: This tells the inbox provider they wrongly classified an email as junk and helps correct future inbox placement
  • Labelling/moving folder: Users don’t take time to manage emails they dont’ want. An email that is manually classified is seen as a good email.

Conversely, Gmail counts these behaviours as bad. They weaken your reputation and threaten inbox placement.

  • Delete without reading. An email that is deleted without reading is an unwanted email. This is different to an email deleted after reading – that’s fine.
  • Mark as junk. A strong signal that the email is not wanted and the sender is sending spam in the eyes of the user

Consider how customers got onto your list. Should someone provide their email address for, say, a quote, and it’s not clear they will also get marketing too, it will cause poor engagement. Purchased data is the worst, not only causing high complaints, but high bounce rates and spam traps.

Authentication (SPF, DKIM) is listed seventh. However, as SPF and DKIM are straightforward technical setup there is no reason not to have these in place and in reality these are must do items. All good ESPs have support for SPF and DKIM.

Data over content

The first place to look when email delivery is a challenge is your data, not your content or sending infrastructure.

Consider these important data questions:

  • Where did your data come from? From organic sign ups, competitions, purchases?
  • How was expectation set in terms of how the address would be used and what would be sent?
  • Has any old data been reintroduced?
  • Has data always been well managed?
  • Has unsubscribed data been accidentally re-introduced?
  • Has the unsubscribe process stopped working?
  • Has purchased data been used at any point?
  • Are hard and soft bounces being removed?

Keeping a record of data sources is not only good for marketing performance, but also for deliverability. If you need to purge data to improve deliverability, then removing the less active data from the most risky sources first is a good strategy.

If you have squeaky clean data and emails are expected by recipients, then your balloons should not burst. The other factors such as content can play a part, but typically only if your data is not in perfect order.