10 Tips to Avoid Spam Filters

To all of us out there who do outreach, spam represents a legitimate threat to our business endeavours. Usually not because we are doing a poor job at writing emails, but because Internet Service Providers and Email Service Providers are brutal at scanning emails in search of spam content.

Studies show that only 79% of emails sent by genuine email marketers reach people’s inboxes. Which means that 21% of emails sent by us, honest and good-willed marketers, end up either in the 9th circle of hell (16%) or get lost somewhere along the journey (5%).

This actually tells us how only a small error is enough to damage our credibility and sender reputation.

Spam mail is so despised by email users that all major countries in the world have passed laws and legislation against it. The American CAN SPAM Act of 2004 and Canadian CASL of 2014represent the leading countries’ attempts to protect people from unsolicited bulk mail. And along with ISPs and ESPs they seem to be doing a good job.

Maybe even too good, if you consider the fact that 16% of emails end up in spam even though their content is not spam-worthy 🙂

Yep, only a small mistake is enough to send an email to hell. And spam indeed is hell as it negatively affects your deliverability rates, sender reputation and might, in the worst case scenario, get you blacklisted.

So without further ado, here is what you should and shouldn’t do to avoid spam.


In Internet communication etiquette, using all uppercase letters is considered rude and disrespectful. What’s worse is that it is perceived as shouting. So avoid using all uppercase letters if you don’t want to annoy your prospects, or alarm spam filters.

This is especially important when you write subject lines. In a research conducted by The Radicati Group, the majority of the people surveyed, 85%, showed preference of an all lowercase subject line.

So always make sure your subject line DOES NOT look like this:

2. Don’t Use Multiple Exclamation Points or Weird Symbols

Again, this one is especially relevant for the subject lines.

A [good] subject line needs to draw lead’s attention, it needs to inspire the lead to open the email. Of course, you first thought might be to use exclamation points and symbols like %, #, $. Because what creates drama and sensation better than visual symbols and “!!!”, right?

No. These will instantly alert ISP and spam filters.

Moreover, studies show that email subject lines that end in a question mark have 44% higher open rates than those that contain exclamation points. So opt for a question, or a witty, inquisitive subject lines and NOT:

3. Steer Clear of Spam Trigger Words

This advice is relevant for both subject lines and email content.

As you all probably know, there exist certain words that have been blacklisted owing to their overuse by spammers. These include words such as ‘free’, ‘best price’, ‘cash’, ‘no obligation’. Spam filter technology scrutinizes each subject line and email body looking for exactly those words.

So stay away from spam trigger words.

4. No to Rich Media Content

More often than not, email clients have the option of viewing media content such as Flash and video embeds disabled. So, it is a good idea not to insert them in your copy at all. Because if they don’t show or work properly, the email will seem sloppy, messy and spammy to your clients. This can damage your credibility.

If the media content is important for your marketing efforts, you can upload it on your website and put a link to it in your copy.

For example, if you want subscribers to see a video, you can use an image with a play button that, once clicked, will lead your clients to the particular video on your website, like this:

Also, you will probably want to avoid using JavaScript and other dynamic scripts, as they will alert the spam filters. And not only that, but many email users won’t be able to load images you insert. So they will simply give up reading your email, or mark it as spam.

5. No to Attachments

Attached files, like PDFs and Word documents, alert spam filters immediately.

Attached files also increase the size of your email. So, it takes them longer to load, which in consequence alerts spam filters.

However, if the document is important for your marketing endeavors, it would once again be a good idea to insert a link or a CTA that leads to the particular document’s location on the website.

But always make sure that all your links work properly and complete the desired action without any problems.

6. No to Irregular Fonts and Rainbow Colors

People pay a lot of attention to the fonts and colors used in the email copy.

A study by Radicati Group tells us that over 60% of people find it unacceptable when email marketers use irregular fonts, different font sizes and font colors. And over 70% of people opted for one size fonts emails.

Here’s an example from HubSpot of what NOT to do:

Finally, spam filters agree on this one with the people, so irregular font colors and sizes will annoy them, along with the invisible text (white-font-on-the-white-background tricks). So don’t!

7.  No to Too Many Images and What to Do With Them

Including images in the email copy is okay, as long as they serve a certain purpose and you don’t overdo it.

Too many images (especially stock images), or too big images create similar problems as attachments. They increase the load time of your email, which negatively affects deliverability rates.

So always make sure to include images that are relevant to the content and complement it. Resize them if necessary, but take special care not to damage their visual integrity. And always, always, always host your images at credible services.

But the problem with images doesn’t end here.

In much similar fashion as media content, some email users, and ESPs, block images as well. And, if your images don’t show correctly, your email will trigger spam suspicion in both people and spam filters.

For example, making your copy in the form of one big image can get your email stuck in spam. Microsoft Outlook doesn’t recognize background images so this email wouldn’t be displayed properly:

Incorrect display of images can turn into a huge problem when you design your CTA as an image. To users who block images, your CTA will look like this:

Needless to say that your subscribers will not get the message which kind of ruins the point of the email altogether.

To prevent this from happening, you should always include alt text to your images. Then, at least, the text will be displayed.

With alt text, the CTA will look like this:

Alt text is easily edited in the text editor, or you can enter it manually in the HTML editor.

8. Do Make Two Versions of the Email

By offering both HTML and plain text emails, you appeal to different people, but you also establish legitimacy with the ISP.

So take time to craft both version of your email. The plain text version lets you be, well plain and simple, whereas the HTML version lets you practice your designer skills you never had the chance to use (just don’t overdo it).

Here’s an example of both a plain text and HTML email taken from HubSpot:

But, with HTML, always make sure that your code is correct. If your email includes broken or incomplete tags, the spam filters probably won’t let it through to the inbox.

9. Do Be a Grammar Nazi

Yes, I know, nobody likes to be corrected when it comes to spelling and grammar. But in email marketing, this is absolutely essential.

Incorrect spelling and faulty grammar will make you look incompetent and unprofessional, which will consequentially damage your credibility.

The Radicati Group study shows that 80% of the surveyed agree with me, and find grammar and spelling errors a capital emailing offense.

What’s worse is that these errors are also major spam triggers.

So don’t be lazy and take time to proofread and edit. You can even use apps, like Grammarly, that do the checks for you. Correct spelling and good grammar will create the air of professionalism and trustworthiness which is something essential for doing good business.

10. Do Let the Unsubscribers Go

Because if you don’t, you might be severely fined.

One of the main postulates of the CAN-SPAM Act is that you should always provide the unsubscribe option.

If people want to unsubscribe, let them, and make their journey easy by making it a one step process. Respect their wishes and never email them again.

Here’s an example from my own inbox that illustrates where to insert the unsubscribe button:

If you do continue to send them emails, they will probably them as spam, which will hurt your sender reputation and reduce email deliverability.

So include an unsubscribe button or link in each and every one of your emails to protect your reputation and credibility with your clients, the ISP and the law.

As you all figured out, these are the dos and don’ts in the email writing process. If you abide by them, the chances are you will be in those 79% of people whose emails end up in email heaven.

Remember, the devil is in the details so pay attention to them!

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