After upgrading to version 18.1 of my online database I am having problems connecting to the custom SMTP server. 

Support advised me to review the configuration via ticket, I did it but the problem remains. Has anyone had the same problem?

The error message is:

The server rejected the test recipient (noreply@odoo.com) with the error 'X-Warning: n.n.n.n is listed at SPauthBL (127.0.0.11)'

I deleted all the settings and entered a new setting for my SMTP server, after re-entering all the data the connection test worked and I was able to send all the emails.

This morning the problem recurred again without me having ever changed anything in the configuration of my mail server.

Can you help me?