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How Does a Spam Filter Work?

Published: 11th February 2021
If you are sending out marketing emails for your business, then the chances are that you’ve already run into issues at some point with getting your emails through to your recipient’s inboxes.

It’s really common for overzealous spam filters to send anything that looks like it might be a marketing email into the junk folder. The job of a spam filter is to remove any unwanted spam emails, but it’s pretty common though for your marketing emails to people who’ve asked to receive them to get swept up and filtered.

This is a real problem for email marketers, because if people aren’t seeing your mailer, then they aren’t going to interact with it or convert into sales.

Help is at hand though, luckily there are steps that we can take to fix this. So, if you’d like to make sure that your emails are hitting inboxes, then watch the rest of this video as we outline the 5 points that play a major part in the delivery of your emails.

Spam Phrases



A spam filter will read the subject header line and the body text of an email, it will screen the contents of this text against a database that it holds of spam type phrases. These phrases are typically associated with text seen in unsolicited sales emails previously.

This does mean though, that if a spam filter is making it’s inbox placement decision based on the inclusion of any sales related words in your email - then you are running a significant risk of ending up in the junk if you mailer has a quantity of these.

So, prior to sending out your email, it’s worth removing any words or phrases that look to sales oriented. These could be; promotion, discount, offer, free etc. Alternatively, to thoroughly clean your text, use an online survive that will screen your text using the same spam filter algorithms. Yes, this is a shameless plug, but our software will do this for you.

Use of Images



If you are selling a product pr a service, then the chances you that you are using images to help present it in your email. Not just product images though, you may be using your company logo and branding in image form. Well, the bad news is that spam filters are on the lookout for image-based mailers, and can class your mailer as spam on this basis.

Does, this mean that we can’t use images if we want decent deliverability then > well, no it doesn’t, but it does mean that there is a little bit of tweaking to do to make sure our mailer doesn’t end up in junk if we are using images.

One of the main things that spam filters are looking for is large file sizes, images typically have quite large file sizes. So, what we need to do is to make sure that the file size is as small as possible - ideally underneath 200kb. There are some great web-based services such as tinypng.com that will do this for you.

You also need to make sure that the amount of images that you are using is counterbalanced with the amount of text, for example, make sure that your mailer contains more text than images. Hardly any text and lots of images is often a real red flag to a spam filter.

Send from Address



Again, this is another big one, the email address that you are using to send your email marketing plays a huge part in what the spam filter is looking at. We know by now, that a spam filter is looking to target an email that it thinks might be a marketing email, as such, they are looking at the send from address.

If you are using a mailbox such as marketing@, sales@ or even worse, no-reply@ then this alone is often enough to trigger a spam filter.

The send from address plays a huge part and luckily, optimising this is a real quick and easy win to put in place. With your next email marketing campaign, if you are currently using a generic address such as marketing@ - try changing it to a personalised address such as your name@. Try this and watch your open rates increases, as more people are seeing your email.

Domain Verification



If you are sending out your email marketing using software to create broadcasts, then this one is really important. Your software will make sure that all of your emails will appear as being from you (by displaying your email address). They will however really be sent via your provider - but that part is not visible.

A spam filter will be able to see that whilst your emails appear as benign from you, they are really being sent via your software are provider. What domain verification entails is adding a small text record to your own domain name that adds a seal of authenticity. A spam filter can see this and it then helps to provide the necessary comfort to pass the security measures employed by spam filters.

Sender Reputation


When your recipients’ spam filter receives your email - it can also see your sender reputation, this is a percentage based score that is calculated by your previous activity. If the score is low, then this results in a fast pass straight into the junk folder.

This score is calculated by organisations such as senderscore.org, the factors that make up this score are, previous spam complaints, people marking your email as spam, reads, clicks and bounces.

For example, if you bounces and spam complaints are high and your reads and clicks are low, then this will result in a low score. Conversely, if your bounces and spam complaints are low and your reads and clicks are high, then this will result in a higher score.

So, the fix here is to clean any dead data from your list, only send emails to people who have asked to receive them and make sure that your content is fresh and relevant to your target audience. A strong sender score always converts to really good inbox placement.

Summary



Ok, so we’ve outlined 5 quick points that if you implement them with your email marketing will make a significant difference. Inbox friendly emails mean higher engagement and higher sales conversions.
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