Admin cannot add a domain to the domain block lists in Org settings. Error 'Invalid or duplicate email address' occurs.
- Org settings - General:
Block creation of prospects with specific email addresses
Block all emails to specific email addresses
Check if there are already duplicate entries in those lists, because if there are, that will
prevent the addition of any new entries.
Then, remove all the duplicate entries and, after that, add the new entries.
There are already duplicate entries in one or both of the block lists.