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 that they end up in spam.

This is not an error from Infomaniak, 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 this domain. If your domain does not explicitly authorize Infomaniak's servers, emails sent from these servers may be blocked or considered suspicious.

Infomaniak now reinforces its controls and directly rejects emails that do not comply with SPF rules, to avoid your emails 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 receive the error that led you here.

How to fix the issue?

To correct this problem, you need to modify the DNS configuration of your domain, that is, the technical parameters that define how your domain works on the Internet. You need to add or update a TXT type record called SPF.

Refer to this other guide to access possible corrections and allow the proper sending of your emails.

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