def validate_no_duplicate_destinations(destinations):
    """
    Validates destinations do not overlap accounts for the same plugin (for plugins that don't allow duplicates).
    """
    dest_plugin_accounts = {}
    for dest in destinations:
        plugin_accounts = dest_plugin_accounts.setdefault(dest.plugin_name, {})
        account = get_plugin_option("accountNumber", dest.options)
        dest_plugin = plugins.get(dest.plugin_name)
        if account in plugin_accounts and not dest_plugin.allow_multiple_per_account():
            raise Exception(f"Duplicate destinations for plugin {dest.plugin_name} and account {account} are not "
                            f"allowed")
        plugin_accounts[account] = True

    Validates destinations do not overlap accounts for the same plugin (for plugins that don't allow duplicates).
    
lemur/certificates/service.py