appengine.standard_python3.bundled-services.mail.flask.main_test: test_send_receive failed

[flaky-bot[bot]]

Note: #11013 was also for this test, but it was closed more than 10 days ago. So, I didn't mark it flaky.

---

commit: d1d77c5a323daeeee90a9f40d5efd66a7d7a6b04 buildURL: Build Status, Sponge status: failed