We recently saw difficulties passing the standard 2N SMTP settings through a new Araknis Router. However, this was related to a new Starlink install. Starlink by default blocks port 25 used for SMTP:

Using Port 465 and SSL rather than the default STARTTLS in the 2N settings and adding it to the 'Services Management' section under ACLs tab in the router makes it work. The email provider needs to accept SMTP Mail using SSL and Port 465 as well.