Error:
IMCEAEX-_O=domain_OU=EXCHANGE+20ADMINISTRATIVE+20GROUP+20+28FYDIBOHF23SPDLT+29_CN=RECIPIENTS_CN=user@domain.de
#550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ##
solution:
Creating an X500 entry under E-mail address
/O=DOMAIN/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=user