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

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

Infomaniak is now strengthening its controls and directly rejecting emails that do not comply with SPF rules, to prevent your emails from being rejected or considered spam by your recipients, or that the servers are misused.

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

How to fix the issue?

To fix this problem, you need to modify the DNS configuration of your domain, i.e., the technical settings 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 find possible solutions and ensure your emails are sent correctly.

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