What Is an Email Firewall?

email deliverability checklist cover
At Warm, we worry about email deliverability.

As you may imagine, the idea of an email firewall is quite ominous to us.

In this article, we’ll go over what an email firewall is, how it works, how it affects deliverability, and how you should go about avoiding them.

What Is an Email Firewall?

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An email firewall is an additional layer of protection for email providers.

They monitor and filter emails from addresses to protect users.

Their main purpose is to reduce and prevent spam, which often comes with viruses or malware.

Additionally, many of these applications provide features that scan inbound emails associated with multiple accounts from different domains and have customizable tools that permit users to block certain domains.

Sometimes, emails get sent to spam folders instead, and users can recover them from there.

For salespeople or marketing specialists sending out several campaigns, however, this is not an ideal scenario.

How Do Email Firewalls Work?

Email firewalls work by filtering out incoming and outgoing email traffic, based on a set of parameters predetermined by the firewall administrator.

As you can imagine, different firewalls will work differently based on the parameters set by the administrators.

But one thing they do have in common?

They all monitor the behavior of other users on the same network server, though. So, if one user is continuously marking your emails as spam, the information is communicated to other firewalls.

How Do Email Firewalls Affect Deliverability?

Your emails continuously being marked as spam by even just one user will begin to have ripple effects when the firewalls communicate.

The more often you land in spam, the higher the chances you have of permanently damaging your senders’ reputation, which is not something you want.

Slowly, your email address or domain becomes part of a blacklist of problem senders, and this may begin to impact your cold email deliverability for other emails that are not part of this particular firewall network.

Next thing you know, your next email deliverability test has you hitting spam for G-Suite and with very low numbers for your senders’ reputation.

Climbing back up from this takes time which you typically don’t have in sales or marketing, so the best thing to do is to avoid the issue entirely.

How to Avoid the Email Firewall

The name of the game in email deliverability is avoiding landing in spam at all costs. When it comes to the email firewall, here are our suggestions:
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Keep your sending lists clean and updated

Make sure that your lists are clean and as up-to-date as possible.

Take some time to look through the lists biweekly to make sure people are still where they are in the correct role.

If they have changed and your email bounces or their new role no longer applies to your product or service, you want to remove them as soon as possible.

Do not give them any reason to mark you as spam or for emails to bounce.

Domains or email addresses sending emails out to addresses that often bounce is information that servers and email firewalls can share with each other.

Spammers will send to several addresses at once and do not care to keep their lists clean, as they are focused on numbers.

You do, because you want to reach actually interested parties.

Demonstrate it to email firewalls by keeping your sending lists updated and as clean as possible.

Avoid spam words or use of images, attachments, special characters, or text formatting

Anything that may trigger an additional spam filter or that your prospects may read as spam should be avoided.

No spam words such as free trial, special characters or text formatting. For both spam filters and people, these are indicators of spam or malware.

Additionally, avoid the use of images, attachments, or hyperlinks anywhere in the text.

It may be tempting to send out white papers or sign up links, but when you’re running numerous campaigns, it ends up being more detrimental to your deliverability than anything else. Only start sending additional content once you’ve ensured their responsiveness and interest. Anything before that will be seen negatively.

Signatures should also be as clean as possible, so that your prospects are more likely to receive the email in their inbox.

A good way to do this is to create a separate address purely for sending out emails. Keep your official signature and email for internal issues or existing clients separate from the email you use to send out campaigns.

Provide value with every email

Because this is heavily based on your prospect's opinion of your email being spam or not, you need to ensure that you provide value with every email you send out.

Follow best practices for cold emailing:

  • Have an intriguing subject line
  • Write a personalized introduction
  • Keep it short, sweet and to the point
  • Demonstrate your knowledge of your prospect and their pain point
  • Explain how your product or service works and is the solution to their problem
  • Have a clear call to action

Do not overdo it with word count or come across as too sales-y or even too heavily personalized. You don’t want your prospect to feel stalked, just recognized.

Remember that your goal at this stage is to educate, improve brand awareness, and to network.

Value is what will differentiate you from spam.

Ensure your target audience is correct

And a great way to make sure your messaging provides value is ensuring your target audiences is correct.

You check the emails biweekly, make sure their roles remain the same and that they still represent the audience that fits your ideal customer profile (ICP).

The best way to get sent to spam is to email people that do not need your product or service.

Avoid that entirely by testing and making sure you’re always reaching out to the right people.

And in conjunction with this, make sure you are segmenting your emails and messaging accordingly.

Roles, industries, and responsibilities are all different enough that you can employ different approaches. Whether that is by messaging or outreach style, different types of messaging will provide you with valuable insight into the customer’s mindset and inform your future steps.

It can open new verticals too, and serve as a way to network for another opportunity!

Warm up your email to increase your engagement rate

Having a high engagement rate is a key factor in maintaining your senders’ reputation.

For that, you require prospects to be responsive. And you ensure responsiveness by lowing the steps outlined previously.

However, you are probably sending out a lot more emails than you will ever receive responses from. This will make email firewalls and similar systems read you as a spammer.

How to avoid it?

By making use of a warm up tool such as Warm to increase your engagement rate.

The tool artificially creates conversations between your email address and others that go on for several chains. And it creates new ones.

Manual seeding is great, but with Warm, your initial email warm up process for a new domain, address, or reviving an older one becomes significantly easier.


Email firewalls will continue to exist so long as spam does.
And they’ll get stronger.

To avoid them and ensure your emails get read, follow the suggestions above.

And remember to join Warm’s launch list to receive further information about email deliverability to help you out!
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