Understanding bounces and suppressions


Sometimes your emails won't get through to your contacts' inboxes. When emails fail in this way, they're known as bounces. When this happens, we'll let you know why something has bounced. You can access this information in Engagement Cloud by going to Reporting > Campaign reports. After clicking on the campaign you wish to investigate, you will see bounce-specific information in the chart under the 'Delivery report' heading.

Hard bounce vs soft bounce

A hard bounce is an email sent to contacts whose addresses are permanently unreachable, most likely because they, or the server they were hosted on, don't exist. The email address is invalid. A hard bounce will immediately result in the email address being placed in the suppression list.

A soft bounce is an email sent to contacts whose addresses are temporarily unreachable, possibly because their mailboxes are full or their mail servers are having temporary issues accepting email. It doesn't necessarily mean the email address is invalid.

Read a detailed explanation of the different types of bounces » 


If an email address hard bounces once, or soft bounces too many times, it will be suppressed in your account to prevent you from sending to it. This helps to protect your sending address and server from being blocked for spamming.

The platform allows you to set how many times a contact can consecutively soft bounce before they become suppressed in your account.

Soft bounce count resets

The soft bounce count for a contact gets reset to zero if:

  • The contact opens an email campaign sent from your account. 
  • The contact subscribes to your account again.
  • The contact becomes automatically unsuppressed (see below).

Automatic unsuppressions

If a contact on the Global Suppression List (GSL) engages with any email campaign:

  • We remove the contact from the GSL if they were added because they hard bounced, soft bounced, or had no MX record. 
  • The contact’s global soft bounce count resets to zero.

Additionally, contacts are removed from your suppression list after a year if they were suppressed because they reached your soft bounce threshold.

When contacts are unsuppressed for any of these reasons, they aren't automatically added to your account - but they can be created or uploaded again.

Bounce and suppression types

At various points in the system you may see references to bounce types. These are explained below.

  • Globally suppressed: Contacts who've either complained directly to us in the past or are known spam traps.
  • Hard bouncers: Contacts whose addresses are permanently unreachable, most likely because they, or the server they were hosted on, don't exist.
  • Soft bouncers: Contacts whose addresses are temporary unavailable, possibly because their mailboxes are full or their server is having temporary issues accepting mail.
  • ISP complainers: Contacts who've submitted spam complaints to us via their internet service provider.
  • Mail blockers: Contacts who've received messages that their provider does not want to process, possibly because of attachments.
  • Domain suppression: Contacts whose email domain you have previously added to your suppression list.
  • Soft bounce: The mail server that handles mail for this email address didn't accept the message when we tried to send it; however, trying again later may succeed.
  • Soft bounce - DNS failure: Although we tried several times, we were unable to determine which mail server is configured to accept mail for this email address. This may be due to the correct mail server undergoing maintenance at the times we attempted to send the message.
  • Soft bounce - mailbox full: The recipient's mailbox is too full to accept the message you tried to send them.
  • Soft bounce - message too large: The recipient's mail server won't accept a message of this size.
  • Bounce - no email address: A bounce came back, but the mail server we sent the message to didn't indicate who the bounce was on behalf of. We've identified the intended recipient, based on the content of the message being returned.
  • General bounce: The mail server returned the message to us, but didn't indicate a reason why.
  • Mail blocked: The mail server indicated that it didn’t want to receive the mail. No reason was given.
  • Mail blocked – known spammer: The mail server has decided that your message doesn’t satisfy their filtering criteria, and thinks it may be spam. It has been rejected.
  • Mail blocked – relay denied: The mail server says that although the recipient’s domain is pointed at it, it won’t currently accept mail for that domain.
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    Thank you, very helpful response. Jonathan, New College.

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    Very useful - would be even more usefullerer if you could include all the bounces/suppressions listed by the API though (eg. spamtrap, blockedlocalpart, deleted, directcomplaint, pendingoptin) - hint hint :)

    Nice one!

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    Thanks a lot.

    This is very useful information.

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    If you recieve a high soft bounce rate does this indicate that your emails are containing words that are triggering spam filters?

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    Hi Joanne,

    Hitting spam filters would in a large number of cases not trigger soft bounces, your email would just get 'dropped at the door' (with no bounce at all).

    It's worth having a look through your bounce reasons. This time of year users can see an increase in soft bounces due to DNS failures just because they're emailing Christmas greetings to people you haven't mailed since last year and the email addresses no longer exist or don't recognise you; keeping regular sending habits can prevent this.

    If it's unusually high, our support team or your account manager may be able to help you debug.



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    Hi Stoo

    Thank you for inserting the different types. One question that actually came to me recently from a client was for us to explain the different soft bounce ID so that they could understand the issues. Obviously I've forwarded a list similar to above but Im sure other whitelabel owners experience similar issues where they would like to have more capability to explain issues.

    Perhaps dotMailer could consider placing some guidance documentation (non branded) that we could use. Might help cut down on unnecessary communications to @dotmailersupport or @keyaccounts. 

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    Looking to my Suppression report - What is a DirectComplaint?

    Other than those that have specifically Unsubscribed / complained, can i send one more email to those on the suppression / bounce lists to 'alert' them to their status, as a confirmation type email that they are flagged as not receiving email from us?

    - Or do i need to use another email system to send this email?

    • If the recipients then want to choose to get off the suppression list is there a mass way to do this or it is one-by-one via a sign-up form based from your contact forms Dotmailer can create...? 
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    Hi Mark,

    A direct complaint means a recipient of your email has complained directly to either us, a hosting facility or possibly even a blacklist about receiving your communications.

    Contacts on suppression lists are placed there to ensure they can't be sent any further email, which is done to protect your, and our, reputation and deliverability rates. Therefore we'd strongly advise against attempting to send any further email to suppressed contacts, even with another system. This complies with email best practice. We have your best interests in heart and we don't want you to get into any trouble!

    However, if recipients wish to come off the suppression list, then that is a different matter of course. There isn't a mass way of doing this, no. As you said though, contacts can be taken off the suppression list individually via the resubscribe process - https://support.dotmailer.com/entries/20823696-Resubscribing-a-contact-to-a-campaign-after-they-have-been-unsubscribed

    Here are some further articles you might be interested in on deliverability and best practice:

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    In my sent campaign report - does it show which contacts didn't receive my email campaign as they are on the suppression list?

    Thank you



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    Hi Lu,

    No it doesn't, as your suppressed contacts are removed from your address books upon suppression and thus they can't then be sent to. This in turn means they won't feature in any sent report.

    However, you can check your list of suppressed contacts anytime by clicking on Contacts > Suppressed contacts.

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    Just looking at this as part of cleaning our databases. For the 'known ISP complainers found', is this people who have specifically complained about us in the past, or just people who have complained about other spam emails in the past?


    I'm guessing that there is no argument that we should immediatly unsubscribe all known hard bounces, direct complainers and invalid domains?




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    Is there a way in which we can find out what list a contact was from for a campaign - say, if we have used 3 address books for a campaign?


    This is never indicated in any reporting field, and is also hard for us to identify which address books especially a contact did originate from. It is very hard otherwise to pinpoint their origination, especially for us sorting our raw data excel sheets in office. We have many lead sheets and thus knowing the origination from dotmailer could help us pinpoint these sheets exactly and mark them up for us. Rather than us continually attempting to find the contact out of our many email databases to mark up their status and to note **not add to DM**


    This way we can keep track effieciently from your products. At current, this can be very time consuming, and of course, would make little sense for us to copy many many of the same campains and name them all individually per address book. This wiuld be messy.


    Many thanks,


    Interfax Europe Ltd

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    Hi Shanon,

    I may not have fully grasped what you're after here but I'd recommend using the contact activity report - https://support.dotmailer.com/entries/20645041-Using-the-contact-activity-report-to-view-history-for-a-particular-contact- 

    Here you can search on a contact's email address and the report will return all of the address books the contact is present in, as well as the campaigns they have been sent. Hopefully this will enable you to easily identify their origin.  

    Hope that helps - but if not then I'd suggest contacting support@dotmailer.com for further assistance. They'll be happy to advise you.

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    For the "Mail blocked - Known spammer" type, is this to do with a particular mailing, or based on the address being on some kind of spam list?  I've noticed an increase on our last mailing, but there really isn't anything different to previous ones, nothing obvious that should trigger it.

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    Thanks for the comprehensive breakdown - have had colleagues asking for more detail on what the bounces actually mean.

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    In the case of soft bounces, if the threshold is say, 10... when an email is sent and if it returns from an email address with a soft bounce reason, does the system retry to send that same email more times until it reaches 10... then it is moved to the suppressed list from that one email being attempted at delivery 10 times?
    are you saying that the "10" threshold actually applies to the sending of 10 total "new" emails and if the threshold is reached by sending these 10 different emails and if it comes back with a soft bounce each time THEN in gets moved to the suppressed list.