You could try modifying the string regular expression for msidmOneTimePasswordEmailAddress. If you can't do it via the FIM Portal, try executing the following SQL statements:
- UPDATE FIMService.fim.ObjectValueText SET ValueText = '^(.+@(?!contoso\.com)[^\.].*\.[a-zA-Z]{2,})$' WHERE ObjectKey = 3161
- UPDATE FIMService.fim.BindingInternal SET StringRegex = '^(.+@(?!contoso\.com)[^\.].*\.[a-zA-Z]{2,})$' WHERE AttributeName = 'msidmOneTimePasswordMobilePhone'
Make sure you persist the previous value or backup the FIMService database in case this doesn't work, and you need to revert back.
Note that you will want to form your own regular expression per your organization as the one given above is fairly simplistic.
Hopefully this is an issue that will be addressed in future releases.