Bug 1090281 - Investigate failure in test_setup_and_send_imap_email.py

try to fix the email failure
This method is still used in the following [test].

[test]:https://github.com/mozilla-b2g/gaia/blob/master/tests/python/gaia-ui-tests/gaiatest/tests/functional/email/test_setup_and_send_active_sync_email.py#L64