Email Bounces and how they affect contact eligibility

HubSpot Product Team

HubSpot sends emails on your behalf, and if the email bounces (can not be delivered) HubSpot receives the bounceback message. Email servers explain why the email bounced within the bounce message. The server response is often overlooked by the untrained eye. However, HubSpot has a framework for categorizing these bounce messages.


So what's the point, why bother? Welp, Every time you hard bounce an email it hurts your sending reputation a little bit. A great deal of hard bounces can jeopardize the deliverability of contacts that are not invalid, and want your email. So, HubSpot built this framework to avoid bouncing emails to the same contact multiple times, to shield your sending reputation from unnecessary hard bounces.


Recipients tab bucketing (public).png


Depending on what category the bounce message falls into, the contact's eligibility for future email may change. You may notice the contact in the 'Not Sent' tab for your next email. After receiving a bounce HubSpot categorizes it and contact eligibility for future email can change in one of the four ways below:

  1. The email address is marked as permanently ineligible for all customers. This is called a Global Bounce. It takes three hard bounces within a 60 day period for a global bounce to occur.

  2. The email address is marked as permanently ineligible just for the customer that sent the email, but not all of HubSpot. This is called a Portal Bounce.

  3. The email has bounced, but the bounce message indicates a temporary error, that may be resolved next time. The contact is still eligible for future sends. This is a Soft Bounce.

  4. If the bounce is due to a temporary issue HubSpot will retry sending the email until the message is delivered or 72 hours have passed. This is also a Soft Bounce, but you will see them in the 'Pending' category. Ultimately, these will move to the Delivered category, or to the Bounced category.

There are 17 categories that a bounce can fall in to, and HubSpot categorizes depending on the wording in the server response (aka. the bounce message). Specific keywords indicate certain errors. This is more of an art than a science, as email servers can be customized to throw whatever messaging they want on bounces. Below are descriptions of the 17 categories that a bounce message may be bucketed in.





Hard Bounce Reasons

UNKNOWN_USER - "Recipient didn't exist" - The server response indicates that the email is currently a non-existant address. These happen when a contact leaves a company and his inbox is taken down, or if there is a typo in the email. *

MAILBOX_FULL - "Recipient's mailbox was full" - In this day and age, most inbox sizes are greater than 1GB, and if an inbox fills to capacity it is indicative of an abandoned address that has not yet been officially closed out. These emails will almost never be engaged with. In cases where the inbox has been cleaned out, contact Support to unbounce.

CONTENT - "Recipient's email server rejected content" - Something in the email body or subject was a red flag that spam filters deemed spammy content. Take a look at this article detailing SPAM trigger words. In cases where the content issue has been addressed. Contact Support to unbounce.

SPAM - "Rejected by spam filter" - There is something in the body, subject, or from address of the email that is deemed SPAM by the recipient’s email server. This category is distinct from IP reputation in that it's something specific to the customer's email, or the customer's sender that caused the server to deem it SPAM. If action is taken on the recipients end to allow future email, contact Support to unbounce.

POLICY - "Blocked due to recipient policy" - Email servers have all sorts of security policies that your sending email address needs to pass before it accepts the message. If the email did not pass one of these policies but it is not explicit about which one, this is the category the bounce ends up in. This includes DMARC; DKIM, and SPF authentication failures. If action is taken on the recipients end to allow future email, contact Support to unbounce.

Missing category - "Unsubscribes" and "Marked as Spam" complaints are not necessarily bounces, but we will not send to these individuals again. This wording surfaces in bounce audit files (generated by Support). It can also refer to a globally bounced address if three UNKNOWN_USER bounces from three separate portals within a 60 day time period have ocurred. These individuals are marked ineligible for all HubSpot customers. *


*HubSpot Support can not "unbounce" ineligible contacts within this category without proof the email is valid. Prove the email is valid with a screenshot of an email from that address in another email system like Gmail or Outlook.





Soft Bounce Reasons

GREYLISTING - The email server requires a longer track record of email activity from the sender. Often there is no track record for the email server to verify the sender, and for that reason the email is not allowed until more activity is monitored.

MAILBOX_MISCONFIGURATION - The recipient’s mailbox is currently under reconstruction or is currently down for some other reason. It is not accepting mail at this time.

ISP_MISCONFIGURATION - Internet Service Provider misconfiguration may be an authentication issue on the recipient's side. The user may have to whitelist HubSpot's IP addresses (see the previous bounce reason for steps to resolve that type of issue).

DOMAIN_REPUTATION - The domain used in the from address has a poor reputation, or a reputation that does not meet the standards of the recipient's server.

DMARC - The sender's domain does not pass DMARC and therefore the email does not pass the recipient server's domain authentication security check. Follow these instructions to include HubSpot on your SPF record.

TIMEOUT - The email server timed out, and is no longer accepting email. These exist to protect the recipient's server from overloading.

THROTTLED - The email server has received too many emails from your domain in a short period of time and will not accept any more messages until a grace period passes.

IP_REPUTATION - The IPs that are sending the email have poor reputation. The recipient's email server security settings do not allow email from your marketing IP addresses because their reputation threshold is higher than the sender score of the IP address. If this happens, you can reach out to the recipient and give them your marketing IP addresses to whitelist.



Pending Bounce Reasons

DNS_FAILURE - The recipient’s domain name server settings were misconfigured at the time the email was sent. These issues normally resolve themselves in minutes.

TEMPORARY_PROBLEM - Miscellaneous category of temporary issues. Similar to the DNS failure category, these issues typically resolve themselves in minutes.


So, next time you call or email Support to unbounce an email address, take a look at the bounce reason to anticipate the Support representative's questions. Come prepared with a screenshot of a recent email from the bounced contact if needed, or reach out to the recipient to whitelist your IP's. Let Support know what you've already done when you reach out


Side Note: If you wish to know the current eligibility for all of your contacts Export the Bounces and Unsubscribes from the email dashboard. You can follow these instructions on how to parse out that export to leave you with a list of ineligible contacts. Or, if you have development chops, you can use the GET email subscription status API endpoint. Do not create a smart list with the 'Emails Bounced' property to show eligibility for future sends. This property includes soft bounces, and omits global bounces. For these reasons and more, it is not an accurate representation of ineligible contacts.

18 Replies 18
Not applicable

Hey @paxton thank you for such a detailed / informative post, this is super helpful. 


Could you share some knowledge on how (if at all) deliverability facts differ between Sales Emails sent via the CRM and marketing emails sent with a verified sending domain on the HubSpot Marketing platform? I'm still a little unclear on this. 

HubSpot Product Team

The non-technical difference is that sales emails are typically 1:1 emails whereas marketing emails are meant to be sent out en masse.


The technical difference is the IP address used:

For sales emails the IP that is used is your own, the same IP your email would use if you were to send from your company's Gmail/Outlook instance.

For marketing emails the email is sent over a HubSpot IP. It may be on our shared network or a dedicated IP just for one customer.


Hi, Just added a new contact record and the email address is flagged as "Contact has bounced globally." neither I nor anyone else in my oganisation has sent this person an email yet. 


The email address is This is a Canadian goverment employee.


What gives?


Can I fix it and email them?



HubSpot Product Team

That is a global bounce, it means that we have received 3 unknown user bounces for that address within the last 60 days. It is very unlikely that address is valid based on our previous attempts to send to that address.


If you think it is a false positive please contact support.


Thanks for your reply. It is most certainly a false positive, I had just received an email from this contact outside of the Hubspot platform. It was after receiving this message that I decided to add the contact record to Hubspot and it was immediately flagged.


I will let support know.


The fact that HS assigns hard bounce to mailbox full errors is of concern for us. Why does HS hard bounce these immediately, why not put into pending and or soft bounce? If soemone is away on a 4 week vacation it's very possible for an inbox to be full. 

HubSpot Product Team

@Qt good question. MAILBOX FULL is considered a hard bounce because, most mailboxes utilize cloud storage, and in order to fill up completely, the email has to be unmonitored for a very long time (typically longer than 2 months). If a mailbox fills up it is normally an unmonitored inbox that will never engage in the future. This is why we consider MAILBOX FULL bounces permanent by default.


If there is an instance of a contact that was bouncing and then they cleaned up their inbox to make it deliverable, you can unbounce their email address from the contact record. In my experience, this is not common.


Thanks for the prompt reply! Since hard bounced = inelible to email to again, I still think it's risky making that assumption. I've had mailbox full warnings myself, so I would argue that they should be soft bounced, so that we can attempt to email them again. If soft bounced again for the same reason, then I'd think hard bouncing them would make sense. 


Is there some way to identify all hard bounces in our database? 


Manual requests for unbouncing names for a large database is prohibitive.


p.s. My team and I would welcome a meeting to discuss such concerns with you and our CSM there Grainne.

HubSpot Product Team

@Qt, sending multiple emails to a full inbox can hurt your reputation with Gmail/Outlook, or any of the major ISP's. So although there is an edge case that you could resend an email to a MAILBOX FULL hard bounce and they could receive it, sending again to all MAILBOX FULL's would come at some cost to your overall delivery rate.


Please see our doc on exporting unsubscribes and bounces for your second question.


@paxton @erica11 @Zakiya 

Hi Paxton,

You are making some broad statements in this post:

"In order to fill up completely, the email has to be unmonitored for a very long time (typically longer than 2 months)." 

"If a mailbox fills up it is normally an unmonitored inbox that will never engage in the future."

Do you have any metrics to support these points? That is not what I have observed. A more accurate statement: 

"An email address which has not opened for 2+ months, which then bounces as mailbox full, is unlikely to engage in the future." 

Because right now I am looking at a mailbox full "hard bounce" on my account where the user opened an email the day before. 

TF mailbox full hard bounce.png


TF Opened before hard bounce.png


I recently had a global unbounce done on our account and had 34% of the mailbox full, policy and spam hard bounces come up as false positives. I put up this post: Hubspot's unconventional bounce handling is costing us valuable leads and customers 

If anyone seeing this is experiencing this problem, please upvote this post and contact your CSM to ask for this to be changed. Thank you!

HubSpot Product Team

Hey there, it's not a rule that mailbox full's will always be unmonitored. That said, an unmonitored inbox is so often the reason for maibox full bounces that it should be the general assumption whenever these bounces occur.


Regarding the example you mentioned, without diving too deep into the specifics, it is possible that the contact you were looking at which opened prior to a mailbox full bounce had their inbox fill up in the time between the open and the bounce the next day. They could have an email server that is set up to cap inboxes at a much smaller amount of memory than say a generic Gmail or Yahoo inbox would. Without being an IT administrator at their organization it is impossible to verify. IT teams don't like to share the specifics of how their security settings work publicly for obvious reasons.


Zooming back out, email security settings are customizeable. So there will never be a one-size-fits-all answer when you are talking about deliverability for all recipients. However; Google, Microsoft, and Yahoo-hosted inboxes make up the lionshare of inboxes out there so that is generally the best place to start.


There is also a risk to unbouncing old MAILBOX FULL hard bounces that I should mention. If that contact hard bounced so long ago that it has since been recycled into a spam trap (more than 1 year ago generally speaking) then the address will be deliverable now as a reporting tool for blocklist operators. By emailing a spam trap such as this you will cause that sending IP to end up on a public blocklist which could in turn cause soft bounces for all other recipients of yours. This could also cause soft bounces for any other HubSpot customers that send over the same network as you. Because spam traps are deliverable addresses they would be included in the 34% that you identified as false positives in the global unbounce you had done. Because they are deliverable they are tricky to find after they have been unbounced. For this reason I would advise that you eventually suppress any contacts that do not open from the 34% that you unbounced. Spam traps, by definition, will never engage so eliminating all contacts that do not engage will be the only way to get rid of an unbounced spam trap. 


For more information on spam traps check out this resource recently written by one of the leading experts in this industry, Al Iverson:


Hello, I just signed up for Hubspot, and ALL of my emails are hardbouncing, regardless of the receipient or message content.  I have yet to be able to get a single email through.  I'm currently using Outlook, and all emails show the same error message:


Delivery has failed to these recipients or groups:

Your message wasn't delivered because the recipients email provider rejected it


HubSpot Product Team

Contact Support by phone at 1 888 482 7768 ext. 3 or through the Help tab in the bottom right while signed into your HubSpot portal.



... sounds like your email server's security settings need to allow for a new foreign set of IP's to deliver email:


Either that or it could be the volume of email that was sent to your server at once. Email server's security filters don't like that unless they have a previous relationship with the sender.


Please do not reply on this thread. Contact support with more information for them to give you an exact answer.


Contact Support by phone at 1 888 482 7768 ext. 3 or through the Help tab in the bottom right while signed into your HubSpot portal.


Where do I sent the proof email to have a contact unbounced?


Participant | Diamond Partner

We have IP_REPUTATION 550 error from a whole internet provider here in Italy.


It's the bigger internet access provider in the country, we simply connot ask them to whitelist an ip on your behalf.


There is something we should do ?

Community Manager

Hi @LucianoTolomei,


I would recommend reaching out to HubSpot technical support regarding this matter. They will be able to assist you with best next steps.


Thank you,


Top Contributor

We are receiving hard bounces back due to spam for a lot of emails. I don't understand why HubSpot marks these contacts as hard bounced as they have outlined a spam bounce back is due to the content of that message. Why then would they not allow you to send to that contact again? Definitely need a better process for this. Should surely be a soft bounce. 

HubSpot Employee

Hi @erica11

Bounces typically occur when email recipient servers reject an email message. This can happen for any number of reasons: unknown user/invalid address, mailbox full, policy, spam, temporary errors, etc. One thing to keep in mind with bounces is they happen on the receiving end; the bounce reason is what is relayed back to the sender (in this case, HubSpot) about why the email cannot be delivered. 


You are absolutely correct about hard bounces due to Spam! These bounces happen when the recipient's email server has determined that something in the body, subject, or From address of the email is spammy -- the receiving servers have found reason to not trust the mail, so rejected it. Best thing to do with spam bounces is to ask recipients to whitelist your sending domain and/or IPs. Once they've done so, reach out to HubSpot Support for assistance with next steps! 


HubSpot will automatically drop any hard bounced contact from future sends to protect your sender reputation, deliverability. Attempting to deliver mail to recipients whose servers have already rejected the mail will only result in further hard bounces and degraded deliverability of the shared sending network our users rely on to deliver mail.