The outage affecting email delivery from the PyPI infrastructure for password reset and registration emails has been resolved.

Root Cause:

• PyPI was sending email from cheeseshop@python.org with reply-to cheeseshop@python.org while signing with the domain key for pypi-mail.python.org
• cheesehop@python.org was not a valid reply-to address for the signed domain.
• Domain validation settings which not fully configured.

Effect:

• A significant portion of recipient mail servers rejected PyPI emails.

Resolution:

• A domain was configured specifically for PyPI email (mail.pypi.python.org) with proper domain validation settings.
• PyPI was configured to send from an address within the configured domain (PyPI Admin <admin@mail.pypi.python.org>)
• A valid reply-to address (admin@mail.pypi.python.org) was configured which will be accessible to the PyPI administration team.

Validation:

• All unsent emails were resent via the new configuration.
• Delivery was verified with the logging available from the delivery service.