We have discovered a bug in Gerrit  that allows you to delete your account's Ubuntu One OpenID association if you delete the email from your account associated with that OpenID. When you do this the next time you log in Gerrit will create a new account for you. Fixing this after the fact is currently difficult. We are working to correct this but the required corrections take time.
We would like to avoid these issues in the first place. Please avoid deleting email addresses from your accounts unless you are sure they are not associated with your OpenID. If you would like help double checking that for you please let us know and one of our Gerrit admins can double check.
We are working to make this fixable after the fact, and will try to work with the Gerrit upstream to prevent you from deleting Ubuntu One OpenID associations from your account in the first place. Until then we apologize for the inconvenience.
Finally, this message and others like it are sent to firstname.lastname@example.org. I am sending this email to a much broader set of mailing lists because the service-announce list membership is quite small. All of our users should be subscribed to that list to get important notices like this one. We keep the traffic low and only send mail there when we feel it is important for you to see it.