It’s 2020, or sometime around then. One night, I received an urgent message from a client saying “Shut it down immediately!” Attached was a screenshot of our marketing email in the company executive’s inbox, with the subject line “Fu*k you, Get 10% Off”.
I rushed to my laptop, found the email campaign, and checked that person’s profile, only to discover that they had used “Fu*k you” as their first name when signing up. The dynamic personalization in the subject line picked it up, meaning this was (mostly) an isolated case. But that night, I learned we needed to do some email list hygiene work.
Cleaning up Profanities From Your Email List
The next morning, the first thing I did was compile a brief list of the most common profanities in the English language and check how many users in our audience had them as a part of their first name. The results? 30,000 people out of roughly 2.5 million had a profanity like “fu*k“, “sh*t” etc., set as their first name – about 1.2% of all users.
This number only increased once I acquired a larger list of 2,000 profanities from this GitHub repository. And mind you, this is a large and reputable subscription-based product, not some kind of scammy, shady website
Profanities can be cleaned or prevented in multiple ways:
- Clean data in Excel. First export user data, clean it in Excel, then import it back without any profanities.
- Add input field validation in the registration form. This ensures users won’t be able to sign up or continue to the next step if they use a forbidden word.
- Implement a validation rule in your email platform. By using a templating language like Liquid, Jinja, Handlebars, etc. and webhooks, you can automatically check every new profile, and if you find a forbidden word, set it to a blank value.
- Create an exclusion segment in your email, push, or SMS platform. This is a short-term solution until you get a real fix in place, as it means these users will stop receiving your campaigns.
Cleaning up Emails with a Typo
Typos in email addresses are more common than you think. Go to your email platform and create a segment of users where the email contains “gmail.con” – the number will surprise you.
When speaking of typos, I focus on the domain name and extension – everything that comes after the @ symbol. Gmail, Outlook, etc., domain names are unique, so typos are easy to spot.
I’ve done research across some of my clients to illustrate how common typos are. These numbers are not universal facts for all businesses out there, but they illustrate a good point.
| Client | Typo Error Rate (Emails with a typo / All emails) |
| Brand A – eCommerce – Email collected during checkout | 0.4% |
| Brand B – Subscription app – Email collected during subscription purchase | 1.8% |
| Brand C – Free & Subscription app – Email collected during free account creation | 3.1% |
As you can see, the share of emails with a typo can go up to a few percent of the total list. These emails are useless to you and will only harm your sender reputation as they will bounce when you try emailing them. The good news is that almost all email platforms will automatically suppress these after they bounce once, but if you want to be proactive about email deliverability, consider filtering them out yourself before they do any damage.
We also observe that the share of emails with a typo goes up as the value of the exchange between the brand and the customer goes down. If you’re buying something and you expect shipping updates over email, you’re going to be a bit more careful when giving your contact information (Brand A), than when registering for a free account somewhere (Brand C).
Typos in emails can be cleaned or prevented in the same way as profanities:
- Exporting and cleaning the emails in Excel
- Adding input field validation
- Adding validation inside the email platform
- Creating a suppression segment
You might be tempted to just fix the typos like “.con” to “.com” and start emailing these users, but this is illegal in many countries, so please inform yourself about compliance first.
Cleaning up Users with Temporary Emails
Temporary or disposable emails are single-use addresses that people use when they don’t want to make a long-term commitment to a brand or receive their emails in the future. Common uses are to get a free trial, test a service, or access gated content. One of the more popular services people use is Yopmail.
The reason you don’t want these addresses in your list is that they disappear after a few minutes or days, after which your emails will bounce. The use of disposable emails was not very common in the brands I researched – only 0.03% on average. But, I assume this is a much bigger problem for brands that offer free accounts, trials, gated content, or any kind of exchange where the user commits only for the short term.
Temporary emails are cleaned and prevented using the same four methods mentioned in previous sections. This GitHub repository contains a list of most temporary email domains you can use to create a filter.
The Conclusion
You might have noticed I haven’t mentioned methods like paid email validation and sunsetting. The reason for that is I wanted to shed light on these three overlooked email list hygiene problems and free methods of solving them. They might only add up to a few percent of your audience, but can have some really nasty side effects. From people getting surprising subject lines in their inbox and perhaps sharing it on social media, to high bounce rates and creating email deliverability problems.
I won’t argue that addressing these email list hygiene problems is a must, but I think the benefits are very clear and can help you deliver a better user experience, and boost engagement.