When DEFAULT_FROM_EMAIL env var isn't set, it defaulted to an empty
string, causing every outbound email (receipts, payslips) to fail
with: Invalid address "".
Phase 1 removed the hardcoded Gmail fallback for security. The
cleanest restore — without reintroducing a secret default — is to
fall back to EMAIL_HOST_USER, which is already the authenticated
Gmail address we send AS. That address is always valid when SMTP
auth works, and it's already set on the VM (otherwise sending
would fail with an auth error instead).
Now:
DEFAULT_FROM_EMAIL = os.getenv("DEFAULT_FROM_EMAIL", "") or EMAIL_HOST_USER
Verified locally: when DEFAULT_FROM_EMAIL is unset and EMAIL_HOST_USER
is 'test@example.com', DEFAULT_FROM_EMAIL resolves to the same address.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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