Your emails are being rejected because one of the authentication tests performed by the recipients (DKIM / SPF) is failing. The error occurs only for recipients using Microsoft email services. The same email sent to Gmail or Yahoo, for example, will pass the test.

The issue comes from the way Microsoft tests SPF / DKIM. This problem is neither specific to Odoo nor new, but it was not blocking as long as Microsoft did not require both SPF and DKIM tests to pass for bulk senders. This has been the case for a few months. As a result, legitimate emails are now being rejected because of this issue. Microsoft has acknowledged the problem and stated that they are working on a fix.

In the meantime, a workaround in Odoo is to send emails from your own domain.

This does not mean that the issue comes from the *odoo.com subdomain itself, but rather that the From address and the address receiving bounce notifications must belong to different domains. In most cases, this helps work around the bug on Microsoft's side.

In practice, you should:

1. Choose a domain that you own and have access to its DNS configuration. For this example, we will use: mycompany.com

Note: If you do not own a domain name but are hosted on Odoo Online and use the Website app, you can receive a domain from Odoo (free for the first year).

2. Create a DNS record of type CNAME for this domain to enable DKIM signature:

Type: CNAME

Host: odoo._domainkey

Value: odoo._domainkey.odoo.com.

TTL: 86400 or the highest possible value

Note: if there is no DMARC record on the selected domain, you need to add one:

Type: TXT

Host: _dmarc

Value: "v=DMARC1; p=none"

3. Use the chosen domain as the value for the mail.default.from_filter key in the System parameters. For example: replace dbname.odoo.com with mycompany.com.

4. Use an email address belonging to the chosen domain as the default from alias for the alias domain. For example: replace notifications with contact@mycompany.com.

With this configuration:

• Your emails will be sent from the chosen default address. For example, contact@mycompany.com.
• Bounce notifications and other replies will continue to be sent to the @dbname.odoo.com aliases, so no additional configuration is required on your part.
• Microsoft should no longer reject emails from your Odoo database due to a false negative or timeout during DKIM verification.