This guide will help you to understand and troubleshoot both email and SMS delivery with 10to8.


How to troubleshoot email delivery issues

10to8 sends many thousands of emails per day, most of which are delivered successfully.

However, there are cases in which emails do not arrive in the inbox of the recipient, particularly in corporate environments with enterprise IT.

This guide outlines what 10to8 does to ensure email delivery, and how we can work with your enterprise IT to ensure successful delivery.

AWS Simple Email Service (SES)

We use Amazon's SES with AWS to deliver all of our emails. Many of our emails come from IP addresses managed by AWS. AWS has the following IP address ranges:

We also use dedicated IP addresses for many of our emails:

Please note that these IP addresses are subject to change, and that SPF makes IP address filtering redundant so we strongly advise against IP filtering.

All of 10to8's emails are delivered from addresses with this format:

The long code uniquely identifies the message.


SPF is an email standard designed to prevent email spoofing by allowing domains to announce which IP addresses are allowed to send emails for that domain. This announcement is done with a DNS TXT record, so uses the authority of the DNS system. A bad actor attempting to send emails faked as coming from the 10to8 domain would fail, since their emails would not originate from an IP address approved by 10to8, and recipient email systems could then reject the email.

All modern email systems support SPF verification. SPF is defined in rfc7208.

When one system receives an email from another server, claiming to be for a particular domain, the receiving system can query the DNS TXT records for the domain, read the SPF details and verify the sending server is permitted to send that email.

10to8 has SPF DNS TXT entries for all outbound emails. Our set-up differs from the default AWS SES SPF configuration, so that we can support DMARC.


DKIM is an email authentication system designed to prevent email spoofing by allowing domains to publish encryption keys that can be used to verify that an email is from the person it claims to be from. These encryption keys are public, and are shared as TXT records in the DNS system. A bad actor attempting to send phishing emails would fail this test because they would not be able to generate a valid digital signature for the email.

All modern email systems support DKIM verification. DKIM is defined in rfc6376.

When a system receives an email, the email will contain a digital signature in the DKIM header. The receiving system then queries the sending domain's TXT records to find the public key against which the digital signature is verified.

10to8 uses DKIM verification, with AWS's SES standard configuration.

For more information on SPF and DKIM, take a look at this blog article:


DMARC is a mechanism for domains to set policies and report on email deliveries. This means that recipient email systems send daily reports back to 10to8 about emails that they have received, apparently from, so that 10to8 can monitor attempted fraudulent behavior by bad actors. As with SPF and DKIM, these are configured with a DNS TXT entry. Using these policies, a domain such as can specify:

1) What should happen to emails that fail SPF and DKIM tests - 10to8 requests a report

2) Which email address should reports on failures and deliveries be sent to

DMARC is less widely supported than SPF and DKIM, but is still a vital tool in identifying delivery issues.

10to8 fully supports DMARC. Our DMARC feedback email address is We monitor these reports to identify email delivery issues early on.


While 10to8 makes every effort to guarantee delivery, there can still be problems, especially with email servers that predate modern anti-spam techniques. Several things that your IT team might be able to check are:

1) Do you use SPF and DKIM for verifying inbound emails?

2) Does your system report on errors regarding SPF and DKIM?

3) Do you have auto-forwarding set up for inbound emails? We have seen cases where forwarding an email damaged the DKIM cryptographic signature.

4) Does your system support DMARC delivery reporting? If so, it is possible that your system could report back to us automatically when there are delivery issues, reducing the complexity of fixing the problem.

How to troubleshoot SMS delivery issues 

We use Twilio and other providers with 10to8 to send text messages to your clients to confirm, cancel, and remind them of their bookings.

SMS failure is rare, but there are occasions when clients may not receive the messages you were expecting them to. This article will highlight how to recognise if an SMS has been delivered or has failed, and why it may have failed.

Recognising SMS delivery or failure 

The record of your delivered/failed messages can be found within each booking. Go to "Calendar" to click on the appropriate booking, and view the "Activity" window.

Screenshot showing the appointment activity window

Note the difference between the SMS symbol and the Email symbol:

screenshot showing the 10to8 SMS icon

screenshot showing the 10to8 email icon

When an SMS has successfully been "sent" and "delivered" to your client, you will see a double tick icon underneath the SMS message, as below:

screenshot showing a delivered message with a double tick icon

You may see the SMS message with no tick icon, or one tick icon next to it, which means the message has been "sent", but not yet "delivered"

screenshot showing a sent message with a single tick icon

This can occur if your client's mobile number is correct, but their phone is off or out of signal range. The message will usually be delivered and 10to8 will show the double tick icon after the mobile has been turned on or receives a signal.

When an SMS has failed to deliver or has been "rejected", you will see a red 'X' icon next to the SMS symbol.

screenshot showing a rejected SMS message

Reasons your SMS may have failed to deliver

1) An incorrect mobile number is the most common cause of failed SMS delivery. This could occur due to a client changing their mobile number, entering it incorrectly when inputting details, or including a space or extra character. It may not be obvious, but a space may be included at the beginning or end of a mobile number and could stop the message from being successfully sent.

2) Very occasionally an SMS cannot be sent due to mobile network limitations or carrier content filtering.

3) On rare occasions, our SMS provider could be down, meaning we can't connect to them to get your messages sent.

4) SMS messages can temporarily fail to deliver due to the mobile being out of range, or powered off. 

Troubleshooting SMS failure 

If you don't see a red 'X' icon, but cannot see that the message has been delivered with a double tick icon, please wait a couple of hours, or until you see a red 'X' before doing the following:

1) Check for any obvious errors in the mobile number, and check that it is definitely a mobile number that has been entered. We will not be able to send SMS messages to landline numbers.

2) Check with the client that their mobile number has not changed, and if possible, whether or not they have recently had their mobile phone powered off or out of range.

3) Check our 10to8 service status page for any broad issues:

Contact Support

If you have not been able to resolve your issue by following the steps in this guide, please reach out to our Support Team. Click here to get in touch.