We have two sites, SITE1(barracuda1) and SITE2(barracuda2) (site2site vpn).
With 3 domains domain1, domain2 and domain3.
SITE1 has domain1 and domain2. SITE2 has domain3.
in our organization we have exchange 2016 (on SITE1) coexistence with Exchange Server 2013 (on SITE2).
Exchange has 4 accepted domains (3 for each domain and 1 default). Also exchange has two send connectors, connector1 (for SITE1) and connector2 (for SITE2).
When i am sending email from @domain1 to an external domain, mail passing through SITE1 and barracuda1. It is correct.
When i am sending from @domain1 to an external domain and @domain3 at the same time (Cc or To), mail passing through SITE2 and barracuda2. i think it is not correct.
i don’t know if it is best practice.