Thanks Ehan,
I have re-checked all as advised and:
- Affected customer does have an existing and working email address
- Then Mailbox does exist, and works with other BPs currently being used.
- Then Email template also does exist, and works with other BPs currently being used, but when manually typing it in, I accidentally left a space in the template name, which I corrected, and resolved this issue.
Thanks,
Tony