Hi Keith,
I am not sure what is your current Kentico version, but there was a bug in Kentico 9 which was fixed in 9.0.2 hotfix (https://devnet.kentico.com/download/hotfixes):
Email marketing - Emails couldn't be created without an EMS license -> When using a license other than EMS, creation and editing of email campaign emails led to an 'Access denied' error.
If you use Kentico 10 version, there was similar bug fixed in 10.0.10 hotfix:
Contact management - Subscription error for contacts with a non-unique email on non-EMS instances -> When subscribing contacts (for example to a newsletter), an error occurred for contacts with a non-unique email address on instances without an EMS license.