Email Error: 550 High Probability of Spam. How to Fix It.

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Anyone writing email copy and sending it en masse has come across a few common errors.

From bounce rates to email deliverability fixes and warming up a new domain, cold emailing is not as easy as it seems.

One of the most common errors? Email error 550.

Let’s dive into how to surpass this common hurdle.

What Is 550 High Probability of Spam Error?

550 high probability of spam infographic
Receiving this error means that your email has never reached your prospect’s inbox.
It was sent straight to their spam folder. And it is extremely unlikely that they will read it as a result.

This is because something in either the content of the email or the way it was sent triggered the prospect’s spam filter.

If you are a marketer or salesperson, this type of email can be incredibly frustrating after spending significant time crafting the perfect cold email. But it does protect your mail server from being blacklisted as a whole by recipients, so it does serve a purpose for you as well.

Plus, while it is a bit difficult to truly avoid this message if you are reaching out to many prospects every day, there are some ways to get around it.

Let’s learn how.

How to Fix 550 High Probability of Spam

550 high probability of spam error infographic

Check your email content

The first thing to do is to go back to your email copy and study it.

Check that you have not made any glaring errors in your writing, nor have you included any large images, fancy fonts, links, or bolded or underlined words.

All of these are known spam triggers.

You should also compare your language to a spam word checker. You never know what language might have triggered the spam filter.

While you’re at it, remember to follow the best practices for cold emails:

  • Keep it short, sweet, and to the point
  • Have a clear call to action
  • Personalize as much as possible
  • Appealing subject line
  • Always add value

Check DNS security settings

Once you’ve studied and edited your content as needed, you should run a deliverability check to make sure everything is alright with the Domain Name System (DNS) security settings.

A tool such as GlockApps will be able to tell you if your SPF, DKIM, or DMARC are not set up properly.

These are important components of your email domain that make it recognizable as an entity for other domains. If they are not set up correctly, your domain will immediately trigger a spam filter and your bounce rates will skyrocket.

Enable SMTP authentication

Especially if you are using Outlook, you want to ensure that your SMTP is authenticated properly.

Similar to the above, it is the mechanism through which ISP clients identify themselves to the mail server they are using to send email.

Mail servers only allow email sending by legitimate users, so having this authentication categorizes domains as legitimate users. Only if they are considered valid by the receiving domain will the email make it through.
Without it, they are sent to spam, and you receive the 550 email error message.

Limit the number of emails going out per hour or day

Often times, marketers or salespeople may be eager to connect with as many prospects as possible and overreach in their outreach efforts.

It is best to start slowly, at about 50 emails per day, before ramping up on a weekly basis to 100 or more emails per day.

If you start hitting spam too often, then slow down and ramp up once again, or utilize a warm up tool such as Warm. This helps increase your sender reputation by receiving responses instead of merely emailing out.

You will avoid triggering a spam filter as instead of having a domain or address that is sending out 50 emails per day or hourly, you are sending less and also engaging in conversations. It makes your domain appear more utilized and less likely to be a spam account that is only focusing on sending out messaging.

Give the email a cool-off period and try again

Sometimes it is all about waiting a bit.

If you’ve been hitting a wall with the 550 email error, and you’ve tried all of the above, it might be time to give that address or domain a cooling-off period.

Use alternative outreach channels such as phones or LinkedIn for a bit while you wait, or set up a new domain and address from scratch to see if it was just the older address.

While you’re doing this, keep the domain warmed up with an email warm up tool and do some manual warm up exchanges with colleagues.

You’d be surprised how email deliverability can change after cooling off for just a few weeks!


The number one enemy of cold emailing is spam.

The 550 high probability of spam error is just one example of how this might play out.

And while it may seem as if it is out of our control at first, there are definite steps you can take to understand it better and try to fix it in the future.

Remember that a good first step is to always warm up your email with tools such as Warm.

Make sure to join our launch list – made by salespeople, for salespeople, Warm is about to become a must in every team’s tech stack, and you don’t want to miss out!
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