Erm…
which parts are you in control?
Router < > LibreNMS Host (Synology? Server? VM? Laptop? PC?)
If you have another SMTP server to try on, it would be great to filter out whether it is the settings, or network wide blockage
- Another SMTP server
a) Fails
Host/Network Problem
b) Success
Office365 config problem
If you are on Syno and firewall turned on, please make sure SMTP outgoing is allowed. If you have to ask an network admin… they might be blocks/policies in the network that you are unaware of.
When you click on Test Email, what error does LibreNMS returns you?