Help Center

High bounce rate warning

If you’ve received a ‘High bounce rate warning‘ message this means that the bounce rate for this specific survey has exceeded the threshold in the last 24 hours. Email delivery will be throttled. Respondents can still answer the survey and you can still access the results, contacts, consult the bounce reason, update contacts, etc.

How is it calculated?

Our system automatically calculates the number of emails that bounce in the last 24 hours (i.e. ‘sliding window’ principle). If during this time frame the number of bounces for your survey exceeds a certain percentage, the remaining email invitations that still need to go out are throttled. How long depends on the time it takes for the rolling bounce rate to drop under the percentage again. The system repeats the calculation every hour, always looking at just the last 24 hours. So some of the bounces that caused the initial suspension will be older than 24 hours and will not be counted anymore.

What does ‘throttling’ mean?

‘Throttling’ means that we send out your remaining email invitations in small batches: the first hour 60 emails will be sent. Every hour the number of emails sent is raised by 60 so the second hour 120 emails will be sent, then 180, 240, 300 etc. After 24 hours the throttling will be removed completely.

Unless another high bounce rate is detected in the meantime. Then the throttling will resume at 60 emails. This process will be repeated until your survey’s bounce rate remains below a specific percentage for 24 hours. After 24 hours, your initial settings will come into play again and any remaining emails will be sent without limitations. Unless you had set up email batches yourself. Then those batches will be taken into consideration again.

Why is there a threshold?

The limit is not an arbitrary number, but a threshold established by ISPs (Internet Service Providers). CheckMarket is required to enforce these industry thresholds by ISPs and anti-spam organizations. Excessive bounce rates could cause CheckMarket to be suspended by ISPs, affecting all of our clients. We must maintain a good delivery reputation. We have no choice.

High bounce rates make ISPs (Internet Service Providers) think that an email server is actually a spam server. Spammers often work with a dictionary of names and automatically make combinations of common names to send emails, hoping some will arrive. To counter this tactic, ISPs block email servers that send too many emails to addresses that do not exist on their domain.

It is important to heed these bounce warnings in your account and use them as an opportunity to take a step back and assess what caused your bounce rate to exceed thresholds.

Always use a correct and up-to-date contact list. Use double opt-in to ensure that the email address entered is correct and in use, and don’t use any old and stale email lists.

What to do?

This message is meant to help you by letting you know that your contact list contains too many bounces.

Take action and review the contacts that still have the status ‘included’ and check for typical errors and typos in the name and domain name. For example, addresses ending in ‘.co’ instead of ‘.com’, or ‘hotmial’ instead of ‘hotmail’, etc. Remove any obviously incorrect addresses such as ‘[email protected]’. Making sure that the emails that still need to go out are valid and exist, will prevent the system suspending you again, once sending resumes.

During the import process, common mistakes are auto-corrected such as ‘’ and invalid email addresses will be flagged and not imported. But we cannot automatically catch spelling errors, typos or non-existent email addresses.

It’s important to catch these before the email invitations go out. So open the contact overview and filter on status Included. You’ll get a list of all contacts to whom the invitation wasn’t sent yet. If you can spot and correct faulty email addresses here, the bounce rate when sending resumes will be lower and the chances of getting your email delivery suspended again will drop considerably.

View email delivery suspension warnings as a tool for maintaining and managing your contacts. If you start to notice a trend of delivery suspension warnings in the survey’s activity log, it could be due to a stale list that contains many invalid, unreachable or non-existent email addresses.

Consistently exceeding the threshold for bounces not only means that you are not reaching your targeted audience, but you’re also affecting your (and our) sending reputation. Use the warnings as a cue to take action toward the health of your contact list.

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