Emails not sending

It is crucial that you invest time in keeping your address books up-to-date and legal. Using address books that you did not acquire lawfully is more likely to result in your account being blocked due to high rates of email rejections or errors.

You should also strive to make it obvious in your invitation message why this recipient is receiving the invitation (unless it is patently obvious). A small high quality list of contacts is always better than a larger low quality one.

We do not recommend configuring email triggers to send to email addresses entered into survey answers unless 1) the target of the survey is a known group e.g. your employees and 2) there is a reason for them to enter a valid email address. Many survey recipients do not want to give their email address away and can easily enter a fake email which would then trigger a bounce and could lead to your account being blocked or your email sending functionality to be disabled.

If your email invitations are not sending or some of them show an error in the Invitation page, there are a number of possible reasons for this. See below for the most common reasons that contact list emails might not be sending as expected.

Block list

SmartSurvey maintains a system-wide blocklist where we record email addresses that have previously failed so that we do not attempt to send further emails to them, this is to avoid losing sending reputation by continuing to target old mailboxes. If you attempt to send an email to these addresses, the message will not be sent but a bounce will be recorded against your address book(s). These will show as "Bounced from blocklist" on the Invitation results page.

If you believe these have been triggered in error, please raise a support ticket but be aware that we will not necessarily be able to investigate every single email that is added to the blocklist, it is preferable for you to try and ensure you capture good email addresses in the first place.


Email invitations can be scheduled in the email tool, but note that this is subject to occasional maintenance. You should see scheduled invites sending on time but generally always within an hour or so of the scheduled time. If you do not see any progress after an hour from the scheduled time, please check the status page or raise a support ticket.


In the opaque world of spam prevention, some email providers downgrade the quality of emails that are sent in large batches - they are often assumed to be spam since they are sent to large numbers in a short space of time. To reduce the chance of this, emails are sent in batches of 100 every minute per list. You will, therefore only see 100 sent of your invitation initially.

Note: This restriction means that for large mailing lists, you should assume an overall rate of around 6000 sends per hour.

If this batch limitation is going to cause issues for your survey, you can contact support and request an adjustment to the batching settings. Be aware though that doing so may impact deliverability for this and future sends because of the possible effect on sender reputation.

Tracking Link Needs To Be Open

It might seem obvious but the survey tracking link needs to be open before sending emails, otherwise the recipients would not be able to click through to the survey. The email sending tool will disable the sending of the invitation if it detects that the tracking link is not open/has been closed.

If the tracking link is closed during email sending, the invitation will be stopped at the time the link is closed. Any emails sent before the link is closed will not be affected directly, but respondents clicking on the email link after it's closed will not be able to access the survey.

If the link is re-opened and you wish emailing to resume, you will need to contact the SmartSurvey support team to re-enable the sending.

Temporary and Permanent Errors

The system that actually does the email sending is based on a protocol called SMTP. Because it is designed for the internet, messages are queued and sent asynchronously with the assumption that sometimes emails won't send first-time and will be automatically retried over a period of 4 hours.

Temporary errors 'soft bounces'

Some errors which are temporary are considered "soft bounces". These might include mailbox full or a temporary network error. If these are detected, your invitation will be updated, the page will show a warning icon, which shows the actual error if you hover over it but importantly, soft bounces can be retried by sending a reminder out. Note that a mailbox being full, although a soft bounce, is likely to be an abandoned account. It would be best for you to delete any of these from your contact list as too many could eventually cause your account to be blocked.

Permanent errors 'hard bounces'

Other errors like "mailbox doesn't exist" are permanent and are called 'hard bounces'. When these occur, your invitation will be updated, like soft bounces, to show a warning triangle and the error but unlike soft bounces, a reminder will NOT be sent to hard bounces. Note that any errors that occur for longer than 4 hours could cause a hard bounce to be registered, especially if you are sending many emails to the same service provider. For example, if the service provider has broken their DNS settings or their email server is not reachable, depending on what our sending servers see, these might be interpreted as hard bounces (like "hostname does not exist").

Emails that have not arrived yet

However, there are some scenarios that might or might not resolve themselves and will delay transmission of the email and either eventually succeed or eventually fail.

  • Some email providers perform a basic "attack protection" called greylisting, which usually involves rejecting the email the first time but if it is retried after, say, 1 minute, it will be accepted. Our mail servers will take care of this but it might increase the amount of time it takes to deliver the email depending on how the specific greylisting works. 1 to 2 minutes is common.
  • Some errors like the misspelling of the email address might cause the mail system to not be able to lookup the correct email provider e.g. "" instead of "". The mail server doesn't know if the error is temporary or permanent and will retry a number of times up until 4 hours have passed, at which point, it will fail delivery, usually as a soft bounce.
  • After 10 minutes of an email being delayed, your invitation will be updated to say that delivery has been delayed. This might be something that you can see would fail e.g. you can see a typo, or it might be something that is related to the destination server and you will just need to wait and hope.
  • Although your address book might have lots of different email address domains (gmail, hotmail, yahoo etc.) it is possible that multiple names are actually processed by the same organisation like office365 or mimecast, and treated as a single suspicious batch of emails. For this reason, you might well receive a number of delays, although these should resolve within the first 15-30 minutes as the messages are retried automatically.

Sender Reputation

Sender Reputation is what we use to describe how trustworthy an email sender is to the receiving provider. The details are largely opaque outside of each provider but will be based on things like how many messages from a particular internet address/server have been marked as SPAM or have been sent to non-existent users etc. It might also be based on the content of messages appearing suspicious, especially if they consider your message "spammy".

Some of these things you cannot control and are managed by SmartSurvey but since the email system is shared by all customers, we act very strictly against customers who might cause our reputation to sink, like sending out unsolicited email or anything not permitted by our Terms and Conditions.

There are a number of actions you can take to improve your specific reputation:

  1. Manage your address books, don't keep addresses longer than you should.
  2. Remove failed contacts from the address book so that they won't continue to fail in any subsequent invitation. 
  3. If you are using a sender domain, check a test message in a tool like Gmail or DMARC Analyzer to ensure that the message is correctly "aligned" and DKIM/SPF pass. Currently, you will not be able to align the Return-Path which comes to SmartSurvey but we will create a feature to customise this in the future.
  4. Take efforts to clearly communicate what the survey is and why the recipient is receiving it, making it easy and obvious to opt-out if that is legally required (it usually is). If you try and deliberately make it hard to opt-out, you are very likely to be marked as spam and your invitation will incur Abuse Reports, which might disqualify the invitation and potentially your account from further use until you have contacted Support.
  5. Try and think about the recipient's feelings and not your own intentions when sending the invitation. Is it something that someone would expect to receive? How often would they expect it?

Remember that people can mark something as SPAM even if it is not strictly illegal so the more you consider your recipients, the less likely they will click that button.

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