Email Deliverability


emails bouncing only through hubspot

Hi guys - I'm hoping someone can help me with this one...

we have a bit of a strange issue.

I have noticed a significant increase in email bounces over the past couple of days and the return email states "550 High probability of spam".

however, if we send the exact same email to the exact same recipient via our regular email account, it's not bouncing at all.

The problem with this is that the increased bounce rate from our email domain is now causing issues with our regular emails as well.

Would you know why this is happening only through hubspot and what we can do to fix it?

And just to give an example:
I just created a contact for a client of ours that we have been working with for the past few months, as I wanted to be notified when she opens the email.
This client is expecting our email and we have been happily emailing back and forwards for months without issue.
However, the first email I sent to her on hubspot was bounced due to this error.

I ran our emails through a spam detection platform and we got a score of 10/10.
It says we're not on any blocklists and all of our email settings on the server side are set up perfectly

The bounce email we are getting back is as follows:

This message was created automatically by mail delivery software. A message that you sent could not be delivered to one or more of its recipients. This is a permanent error.
The following address(es) failed:  k******** host  []   
SMTP error from remote mail server after end of data:   
550 High probability of spam
Reporting-MTA: dns; 
Action: failed Final-Recipient: rfc822;k******** 
Status: 5.0.0 Remote-MTA: dns; 
Diagnostic-Code: smtp; 550 High probability of spam

Any insight into why this is happening and/or how to fix it would be amazing.

The increase in bounced emails through hubspot is starting to have an impact on our deliverability outside of hubspot as well, so it's kind of urgent to sort this out

4 Replies 4
Community Manager
Community Manager

emails bouncing only through hubspot

Hi @VisionDigital,


Thank you for reaching out!


If I'm understanding properly, you are experiencing this issue with sales emails (1:1 emails) sent to contacts in your CRM correct? Please correct me if I'm wrong 😊 


When you send a 1:1 email through HubSpot, you are sending the email through your email client's  (Outlook, Gmail, etc) rather than through HubSpot's server which would be the case for marketing emails. 

The "Smtp; 550 High probability of spam" error is likely related to the recipient's security settings and software since it believes there is a high probability of it being spam. This help article goes into further detail on this. 

  • It's possible the tracked links in the email are the cultprit (all emails sent from the CRM directly will be tracked).  The email recipient could try temporarily disabling tracked links in the account to see whether or not that's the case.
  • If the email is successfully delivered from HubSpot with tracking disabled, it suggests the email tracking links applied to the email are the issue.

I would also recommend trying to contact the individuals outside of email to see if they can add your email address to their allowlist, so that their email security isn't blocking your emails.


Hope this helps!




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emails bouncing only through hubspot

We are having the same issue with our outbound email sent from Hubspot. We are receiving a bounce message when we send regular (not marketing) emails to our old contacts. Clearly, the issue is with Hubspot because sending it from Gmail to the same email address works fine. Do you have a solution how to fix this?  


emails bouncing only through hubspot

Actually, this has been tested (kind of).

I added a new email address to our account and sent a few emails from the new address yesterday with tracking in and they all went through fine.


it's just on one email address and only when sent through hubspot as a 1:1 email


emails bouncing only through hubspot

Thanks for the insight.

I will test turning the tracking off and see what happens.

I really hope that is not the case because the only reason we use hubspot if for this feature.

If this does turn out to be the reason, I wonder why everything worked fine for close to 5 years and then the tracking suddenly caused issues in the past couple of weeks.

I will test it and let you know