Namespace sharing between 2 Domains (Exhcange 2010) without contacts.

Hi

following these articles to share a domain between 2 differnent exchange orgs works ok without contacts.

http://exchangeserverpro.com/how-to-share-an-email-domain-between-two-mail-systems/

https://technet.microsoft.com/en-us/library/bb676395(v=exchg.141).aspx

DomainC address is setup as an accepted "Internal relay" domain on DomainA "Receiving" and as Authorative on DomainB.

A send connector is done from DomainA to DomainB.

Mail flow works fine and email is delivered to both orgs and NDRs are also created.

Without using a contact if a user in DomainB sends an email to someone in DomainA using DOMAINC as the email address then delivery fails as there is no connector back from DomainB to DomainA for it to forward this way for checking.

IF a connector is put in back in this direction is there now a definite chance of mail looping ?

thanks for any responses