I've been seeing numerous emails bounce back that didn't have an email address in the "to" field of the message. Further inspection shows that the example user I chose has neither has an email address set up, nor do they have a stale field saying that they had confirmed their email address previously.
Most of these bounce-backs in the past few days have been notifications to new users about "Welcome" messages on their talk pages.
Example for a user created today who bounced an email back:
(The username isn't actually 'RedactedUsername', but that's been substituted in the data)
Bounced back email:
- The following addresses had permanent fatal errors -----
(reason: 550 5.1.1 User unknown) ----- Transcript of session follows -----
550 5.1.1 RedactedUsername <>... User unknown
Final-Recipient: RFC822; @pedlfaster.pedlr.com
Diagnostic-Code: SMTP; 550 5.1.1 User unknown
Last-Attempt-Date: Sun, 8 Mar 2009 14:57:33 -0400
- Forwarded message ----------
From: WikiAdmin <firstname.lastname@example.org>
Date: Sun, 8 Mar 2009 14:57:33 -0400
Subject: LyricWiki page User talk:RedactedUsername has been created by SomeOtherUser
The LyricWiki page User talk:RedactedUsername has been created on
12:57, 8 March 2009 by SomeOtherUser, see
http://lyricwiki.org/User_talk:RedactedUsername for the current version.
This is a new page.
Editor's summary: Welcome, RedactedUsername!
Contact the editor:
There will be no other notifications in case of further changes unless
you visit this page.
You could also reset the notification flags for all your watched pages
on your watchlist.
Your friendly LyricWiki notification system
And the info in the database:
mysql> select * from wiki_user where user_name='RedactedUsername' \G;
- 1. row ******* user_id: [redacted] user_name: RedactedUsername user_real_name: user_password: [redacted for privacy] user_newpassword: user_email: user_options: quickbar=1
user_touched: 20090308185738 user_token: dcacc[some hex chars redacted here]66b7a573c
user_registration: 20090308163239 user_newpass_time: NULL user_editcount: 3
1 row in set (0.00 sec)