Currently, the mail queue has a handful of outgoing bounces that relate to mails to user@tools.wmflabs.org (an existing mail address) that were tried to be forwarded to that user's address, but didn't succeed.

The problem with that is that the recipients of those bounces (i. e. the senders of the incoming mails) are from non-existing domains and/or users.

The mails are in Chinese and contain spreadsheet attachments. User "user" seems to be Chinese, but my gut tells me that this is spam.

So before we become the target of more of that, we should harden the mail server so that it only accepts mail from domains that actually resolve (and/or other similar anti-spam best practices for exim).

Version: unspecified
Severity: enhancement