If you are using your own domain for emails (using an address myself@mycompany.com and you own the "mycompany.com" domain), you should always consider to update your DNS records in order to be SPF compliant and allow DKIM.

See

https://www.odoo.com/documentation/18.0/applications/general/email_communication/email_domain.html

Note that with some providers you have to add a dot '.' at the end of the value for the DKIM to prevent the provider to automatically append '.yourdomain.com'



Once the setup is done, wait for a couple of hours for the propagation and then test it. One easy way to test it is to create a Contact in your database with one of your gmail addresses, to send a message from the chatter of that contact. Then, in gmail, you show the original message and you check that both SPF and DKIM have status 'PASS':

and you should see: