Steps to re-produce:

  • Go to the dotmailer settings page
  • Enter your account details
  • Select a domain that isn't 'all domains' in the domain access section
  • Click save
  • Click the 'Reset all accounts' link
  • You see a success message, but the account details haven't been deleted

The account details aren't deleted because the module uses var_del() when the account details are stored in the domains variables settings and can only be deleted with domain_conf_variable_delete()

Just in case anyone else bumps into this issue.