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Why Emails Get Flagged as Spam -- And How to Prevent It
Oct 15, 2020 | 4 minute read
Getting marked as spam is a very opaque and scary thing. There is no one to call and no reason given for it happening; many times you may not even know whether or not your emails are going to spam.
Getting out of the spam box and making sure it doesn’t happen again can be very confusing. Let’s take a high-level look at why you may have been marked as spam and what you can do to prevent it.
Spam filters have large lists of words and phrases that may be considered spammy. These words may immediately block the email, but more likely the contribute to a score or a distribution that will be considered. For example the spam filter will count the number of words marked as “spammy” and see what percentage of the total content it makes up. The filter will have some threshold at which the email will be marked as spam.
Make sure that you limit any words that may be considered spammy. Pro tip: “Free” is one of these words in most cases. Knowing which words feel “spammy” is fairly intuitive, but you can use little toy projects like this one (Not affiliated with Ashpool) if you want a quick glance at something that might be spammy in your email.
Almost anyone who has sent many email blasts will have a memory of a time when some of the emails seemed to go through… and then the “undeliverable” warnings came back. Some will not have been so lucky as to get the warnings!
Mail servers keep track of how many emails they receive from any given sending domain. They also keep track of the rate at which this changes. If you take an email domain that you only send a couple emails a day out of and then send a blast to thousands (or tens of thousands) of recipients most email servers will reject these. The first few will go through as those are still under the rate the mail server considers spam.
Maintaining a steady flow of emails is an important part of keeping a healthy mail domain. Keeping your blast rates at some small multiple of your daily send rate will keep you below the rate limit of the mail servers you are sending to. Additionally, keeping your daily send rate up will increase how many emails you can send blasts to. This is also why many mailing sequencing applications will send blasts out over some period of time.
Some filters will grab a random piece of your email and use it as a sort of “fingerprint”. This is checked against a database of other fingerprints from known-spam emails, because it is a random section your personalized emails may still match each-other.
Because the fingerprint is a random piece of the email, you cannot get away with only personalizing one peice of your templates. For this reason it is important to change up your templates if you think you are getting marked as spam.
Spam traps are fake addresses that will mark anything sent to them as spam. These are used to weed out spam from non-human (bot) sources. These are usually email addresses at slightly different domains (mycompany.co vs mycompany.com) or other typically typo-based differences. They are hard to detect and will respond as a real email server.
Catch-alls are slightly different but may be used for a similar purpose. If a domain sees a lot of mail coming to addresses that don’t match anything (and are thus caught in the catch-all) it may choose to mark the sending domain (your domain) as spam for a period of time.
While spam traps are relatively uncommon on professional domains, Catch-alls are extremely common. Make sure ‘catch-all’ emails only make up at most 20% of your email blasts. Most enrichment providers only return a ‘verified’ response when checking an email, make sure yours also tells you whether or not the domain has a catch-all. Quick plug: Ashpool will tell you this.
There are domain-specific settings you may not have set up properly on your mailing server. These are pretty technical and only the domain administrator will be able to set them up. These are referred to as SPF, DKIM, and DMARC domain records.
To test whether or not your domain is properly set up, check a tool like MX Toolbox (Not affiliated with Ashpool) for issues like “Missing Dmarc Record”.
These issues alone will likely not mark your emails as spam, however they can contribute to the mail servers you contact trusting your domain and prevent further problems with being flagged as spam.
Not all of these problems are avoidable by using a tool, however there are tools that can help: Ashpool’s Preflight feature automatically verifies email domains and provides information such as whether the domain has a catch-all.
Make sure you’re sending emails to real people, not sending a flood of messages all at once, and that your sending domain has all of its records in order and you should quell any email deliverability problems you have been having.