Gmail loses the html formatting of emails sent with Odoo

Question

My company migrated their CRM starting to use Odoo, and then I proceeded to configure the external mail server (gmail), the @catchall parameter, and then define the odoo mail templates.

So far I have no problems, and everything works as I expect, so the mails are correctly and received. However, I have a problem with viewing the emails ... let me explain. Sent an email through Odoo, I see it correctly in html format, so by accessing the gmail email account via browser and opening the message, also in this case it is correctly formatted and displayed as html.

However, the recipient of the e-mail upon receipt loses the html formatting and therefore receives the e-mail displaying it in plain-text.

On the gmail settings I have already configured to send messages in html, I tried to disable it and then re-enable it but nothing happens.

Do you have any suggestions or advice?