First Email Campaign - "Unknown user" Hard Bounces for Well Known Contacts

New Contributor



We pushed out or first email campaign through HubSpot on September 4th. Didn't really think anything of the bounce rate since they would be filtered moving forward, thought they were once-valid emails that were no longer active. 


I received a call today from a coworker saying that our *internal* email addresses could not be sent email to through HubSpot since they hard bounced on the campaign. We send email to each other very often through the CRM and have never had a single issue with bounces between eachother, yet every single one of our addresses bounced. There is also another contact that is highlighted in the image below that we speak with often and have never had an issue. 


I did verify that we do not have history with the other redacted contacts in the image below, so I cannot speak to them. I navigated to the help document ( for help on how to unbounce our four internal emails, but we do not have the ability apparently unless we upgrade? We CC each other frequently in the CRM when discussing customers, are we going to be bullied into upgrading just to get that functionality back, or is there another way to unbounce our addresses?


Annotation 2019-09-15 120440.pngOur company emails that were Hard bounced


Thank you for your help,



2 Replies 2
HubSpot Moderator

Hi @ericbarber,


I happened to be able to find your contact in the account and noticed that it bounced on a marketing email send on September 4 due to an UNKNOWN USER error. Perhaps the email was invalid or unreachable at the time. The address appears to have bounced on a future send that was sent from a connected inbox on September 15. See below. 


Screen Shot 2019-09-18 at 5.32.50 PM.png

Finally, there was a successful connected inbox send on September 17. Given this timeline, it seems like there was perhaps an issue delivering to this address that has since been resolved. It is possible something similar occurred with the other addresses on your marketing email list that are now successfully able to receive 1:1 mail. 

The unbounce feature is not available in HubSpot Marketing Free accounts. Going forward, you may continue to engage contacts through connected inbox sends. 

New Contributor

Hello @Zakiya ,


Your response is exactly the same as my original question. I know all of those details already which is why I asked the question. 


There was obviously an error somewhere that cause all four of our work email addresses to bounce. They have never failed us since we set up HubSpot, and we send email to eachother frequently through this platform. The fact that they just happened to fail on a marketing email seems strange, since we have these emails tied in to our own HubSpot accounts. They have been working just fine. 


I understand that I can contact customers through connected inbox sends, but we need to contact and CC eachother on emails as well through HubSpot. Could you please unbounce our four work emails for us so that we can continue like we have been doing the past six months? I am the administrator for the site and the emails and have never run into deliverability issues before or after this experience with our work emails. UNKNOWN USER does not give enough information, and if you look back prior to September 4th you'll see literally hundreds of successful sends and receives through those four addresses.