Remove email validation from Feed Import
The validation logic for the email is embedded within the user feeds module in FeedsUserProcessor.inc which means the best way to go about this is to create you own, almost identical, feeds processor in your own custom module. Read up on how to create a custom processor.

After reading that documentation you'll need a processor class and you can use FeedsUserProcessor.inc within the feeds module as a starting point. Copy that file into your own module where necessary, rename it and also rename the class name defined within the file. In this file you should see this implementation of the entityValidate function:

/**
 * Validates a user account.
 */
protected function entityValidate($account) {
  if (empty($account-&gt;name) || empty($account-&gt;mail) || !valid_email_address($account-&gt;mail)) {
  throw new FeedsValidationException(t('User name missing or email not valid.'));
  }
}


Remove the !valid_email_address($account->mail) bit in that if statement and configure your feeds importer to use the custom processor you just created.

FYI, I would not recommend importing users with invalid email addresses as this will cause major problems with your users trying to use your site properly.