Error: No route found to domain DOMAIN from server SERVER/EXTSMTP via server SERVER/DOMAIN

I am trying to set up secured routing between two domains with an external domain within the routing path (INTERNALDOMAIN<>DOMAINSMTP<>VENDORSMTP).

Messages are routing out to the VENDORDOMAIN, but when I trace route, the trace fails with the error “No route found to domain DOMAIN from server SERVER/DOMAINSMTP via server SERVER/INTERNALDOMAIN” (address formatted “CNNAME/OUNAME/ONAME@INTERNALDOMAIN”). I have not yet received a message through this route from VENDORDOMAIN.

I have domain documents:

INTERNALDOMAIN -

(adjacent)DOMAINSMTP

(non-Adjacent)VENDORDOMAIN via DOMAINSMTP

DOMAINSMTP -

(adjacent)VENDORDOMAIN

(adjacent)INTERNALDOMAIN

I have connection Documents:

INTERNALDOMAIN -

(LAN-mail)INTERNALDOMAIN to DOMAINSMTP

(SMTP-mail)INTERNALDOMAIN to DOMAINSMTP

DOMAINSMTP -

(LAN-mail)DOMAINSMTP to INTERNALDOMAIN

(SMTP-mail)DOMAINSMTP to INTERNALDOMAIN

(LAN-mail)DOMAINSMTP to VENDORDOMAIN

I have Smart Host on DOMAINSMTP pointing to INTERNALDOMAIN server and ENABLED for all local internet recipients.

I am at a loss at this point to what I am missing or have mis-configured. Any help would be greatly appreciated (ps - looked though posts, but found nothing relevant to this particular configuration)