When your company sends enough emails, you’ll inevitably run into spam filter issues at some point.
Generally, your company email signature will white-list your company emails as spammers don't use an email signature for obvious reasons.
Evaluating an email delivery issue includes your email server, the recipient spam filter settings, your email subject, your email content/links/images and finally your email signature.
The vast majority of all spam filter issues are caused by email content and is not caused by your email signature. This means that the symptom typically is related to one or a few senders/recipients.
Frankly, it's impossible to answer as only the recipient of your email, can tell you why a specific email is flagged as spam at their end.
In this article, we'll advise general Best Practice guidelines which will help you troubleshoot and fix most common spam filter issues.
How does spam filters work?
Spam filters consider a long list of criteria when judging the “spamminess” of an email. They’ll weigh each factor and add them up to assign a spam score, which helps determine whether an email will pass through the filter. If the score exceeds a certain threshold, your email will get flagged as spam and go straight to the junk folder.
Each spam filter functions a bit differently. This means that your email could pass through Spam Filter A without issue, but get flagged by another Spam Filter B. To make things more complicated, spam filters are typically configured by individual server administrators. Thus, your email could pass the spam filter in one company, but get flagged as spam in another company using the same spam filter (because the two companies use different configuration).
As for that list of spammy criteria, it’s constantly growing and adapting, based on—at least in part—what people identify as spam with the ‘Mark as spam’ or ‘This is junk’ button in their inbox. Spam filters even sync up with each other to share what they’ve learned. There’s no magic formula—and spam filters don’t publish details regarding their filtering practices—but there are general steps you can take to avoid landing in your recipients’ junk folder.
Keep a healthy balance of text and images
Image heavy emails without much text can raise a red flag in spam filters. Although different spam filters have different criteria for a healthy balance of text and graphics, it is recommended to maintain a proper text-to-image ratio to ensure your emails are delivered. Aim at 80:20 text to image ratio as a thumb-rule to be safe (60:40 text to image ratio can be sufficient).
Only use the link to web pages
Having a URL path that leads to a PHP page will get your email filtered as spam with 100% certainty.
Keep the number of links below 6
When you check the emails in your spam folder, you'll notice that they often include a lot of links. Therefore, try and reduce the number of links in your email signature. Having 5 links is normally not a problem.
Keep a healthy balance of the skin and non-skin colors
Most spam filters estimate the intensity of skin and non-skin color pixels in your emails. Especially when you use headshot photos, it's critical to test OK for a few pilot users. We've also seen emails with campaign banner getting filtered as spam because the banner skin color ration was too high.
Create your own image path (URL)
Generally, we recommend using Xink images as we secure that they will not get your email spam filtered.
If you deal with a client that specifically whitelisted your domain, then you should use image path to your own server: