If Unattended-Upgrade::MailReport is only-on-error and a package "has a conffile prompt and needs to be upgraded manually", unattended-upgrades does not send an email to the address configured in Unattended-Upgrade::Mail. This appears to be a regression of #89, which was previously fixed by #92. Bisecting revealed that the regression was caused by b2842bd, which was part of #268.

It would be nice to have a way to get email notifications when packages can not be upgraded due to a conffile prompt, so that administrators are aware of the need for manual intervention on the affected system.

Thanks,
Kevin