Email Error: 550 High Probability of Spam

Your cold email deliverability can hit a wall when faced with error 550 high probability of spam. Learn how to solve it with the best email warm up tools available.
Cold emailing is a great way to connect with prospects, create rapport and generate leads, but it’s not easy. Creating an effective cold emailing campaign takes time, dedication, and strategy.

Fortunately, some tools make this process a little less challenging.

Warm up tools help get your email campaigns in your prospect’s inboxes and avoid the spam folder.

They provide everything to detect your domain’s flaws: such as SPF/DKIM/DMARC not set, to which email provider you're hitting inbox, improve your sender reputation, and warm up your email to hit the inbox effectively. All of which are essential for a successful cold emailing outreach.

What is the 550 Spam Error?

The "550 high probability of spam" is an error that indicates the email you attempted to send has been flagged as spam by the recipient's email server.

This error message is usually caused by spam filters that are in place on the recipient's email server. These filters are designed to identify emails that appear to be spam based on various factors, such as the sender's email address, the email's content, and the email's overall structure.

Suppose you receive a "550 high probability of spam" error message when trying to send an email. In that case, your email was not delivered to the intended recipient because it was identified as spam by their email server.

To resolve this issue, you may need to modify the content of your email and ensure that it does not trigger spam filters. Additionally, you can contact the recipient and ask them to whitelist your email address so that future emails are not flagged as spam.

How to Fix the 550 High Probability of Spam Error?

Check Your Email's 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 or included any large images, fancy fonts, links, or bolded or underlined words.

All of these are known spam-triggers words.

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 ensure everything is alright with the Domain Name System (DNS) security settings.

A tool such as GlockApps can 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 bounce rates will skyrocket.

Enable SMTP Authentication

Especially if you are using Outlook, you want to ensure 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 an email.

Mail servers only allow email sending by legitimate users, so having this authentication categorizes domains as legitimate users. It will go through only if the email is considered valid by the receiving domain.

Without it, they are sent to spam, and you will receive the 550 email error message.
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Limit the Number Of Emails Going Per Hour

Oftentimes, 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 Unfiltered. This helps increase your sender's reputation by receiving responses instead of merely emailing out.

You will avoid triggering a spam filter 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 focusing only on sending out messaging.

If you're sending cold emails, check out our blog post about how many cold emails to send per day.

Give the Email a Cool-Off Period of Time

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 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 always to warm up your email with tools such as Unfiltered.
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