Freelance writing


Content strategy

Email woes

May 10, 2018

Whilst moving a client’s newsletter operation from their existing provider to Mailchimp, I encountered the following message:

“Your list is likely to trigger spam filters, or generate bounces and abuse complaints.”

Little did I know that this vague error message would lead to a world of farce, a 66% drop in the size of the number of recipients but, eventually, a much healthier list.

What went wrong

Email lists rot over time. People become disengaged, email addresses get abandoned, sometimes entire email providers stop working. Without TLC these changes can lead to more and more emails bouncing, which eventually causes problems.

Mailchimp places limits on role-based addresses during a bulk import. These means addresses starting with admin@, support@ or any of 35 similar prefixes are culled. This was the most benign of their problems.

Below is an indicative sample of the rejected emails. Those highlighted yellow are legitimate email addresses, but were rejected for being role-based (see above) or for typos (binternet should be btinternet, hormail should be hotmail, gmil should be gmail).

The red ones are spam email addresses. There is no need to blur these as they are fake, and do not correspond to any real people.

Blurred rejected emails

Next came the spam.,,, all redirect to, “the strongest provider of anonymous disposable e-mail addresses on the Internet!”. is “an email service that allows you to create temporary disposable mailboxes, in a completly anonymous way”. is “disposable email with all the features of a traditional email address!”.

In short, all garbage. Spam that could be malicious, or could be completely arbitrary.

Righting the wrongs

Initially, I thought the 22 email addresses above we the only ones flagged as problematic. Oh, how naive and incorrect I was. As I mentioned, 66% ended up getting culled from a list of well over 1000 addresses.

Rejection after rejection, despite removing addresses that were obviously problematic, made me dig a bit deeper.

I found three tools for checking quality of email addresses in a contact list:,, I went for the first because it provides free information, and because their paid information was cheapest.

The free info breaks emails into five categories:

Email categories

A+, A and B are usable to incrementally less ideal degrees. D and F come with the recommendation to remove them from your address list. Seeing so many D and grades came as quite a surprise.

Further information must be paid for.

Each email address is shown, along with its rank (outlined above) and cryptic coding (each is either NOT-RB or RB, and NOT-DI or DI).

DI stands for disposable: all email addresses marked DI are created by sites similar to those mentioned above.

RB stands for role-based: again, corresponding to above.

Neverbounce was used to recheck. The list with D and F grades, and DI and RB addresses removed was deemed ‘dirty’:

A bounce rate of ~9% is dangerously close to the 10% flag

Removing the B grades ‘cleaned’ the list:

As mentioned, these steps reduced the number of email addresses on the list by 66%, from over 1000 to well below it. The impact was massive.

Some can be re-added (the role-based ones and the typos), which will take it back up slightly, but the drop is still formidable. Permission must also be required for each address added back to the list, otherwise those entries will not be GDPR compliant.

Learning from the mistakes

There are some useful takeaways here:

  • Update your mailing list management software often. My client were receiving bounce rates of <1% for our email campaigns, which differs drastically from the 16%+ being recorded by Amazon (whose servers sent our emails). They got spanked because we violated the rules for a long time without knowing.
  • Look over new sign-ups occasionally. If lots of them are from disposable email address providers, tighten the security on your sign-up process, and ideally cull these manually.
  • Enable 2-step verification for email sign-ups to reduce the number of spammy sign-ups.
  • Check the health of your mailing list every once in a while, to check you aren’t sleepwalking to disaster!