Better mailq template email

[adehnert]

The mailq template email was designed for users who had lots of messages. These days, we're using it for users with like a hundred queued messages. There's no real stability issue, and even the spam issue that generally underlies them are not necessarily severe. We should probably come up with a less doom-and-gloom email for cases that aren't due to spam, and some more useful text for cases that are due to spam.