This guide details the reasons why an email cannot be sent and instead returns an error Sender denied: auth guards failed.

Why an error when sending?

When you send emails from an address like abc@domain.xyz via Infomaniak, it may happen that these messages are rejected by some recipients (like outlook.com) or end up in spam.

This is not an error from Infomaniak, but a security measure related to how your domain is configured. Indeed, each domain has a protection system called SPF (Sender Policy Framework). This system indicates which servers are authorized to send emails for this domain. If your domain does not explicitly authorize Infomaniak's servers, emails sent from these servers may be blocked or considered suspicious.

Infomaniak has now strengthened its controls and directly rejects emails that do not comply with SPF rules, to avoid having your emails rejected or marked as spam by your recipients or having the servers misused.

This means that if your domain does not correctly declare Infomaniak's servers, you will receive the error that brought you here.

How to fix the issue?

To fix this issue, you need to modify the DNS configuration of your domain, i.e., the technical parameters that define how your domain works on the Internet. You need to add or update a TXT record called SPF.

Refer to this other guide to access possible corrections and ensure your emails are sent correctly.

These simple adjustments will notify email services like Outlook, Gmail, or Yahoo that Infomaniak's servers are authorized to send emails for your domain, significantly improving the deliverability of your messages.