If a single user has a null email address, no further daily reports will be sent.

The log file will contain warning similar to the following:

2008-11-27 16:04:00,375 WARN [DefaultQuartzScheduler_Worker-5] [confluence.mail.jobs.DailyReportJob] doExecute Not sending notification email [ Confluence Changes in the last 24 hours+ ] to [ John Doe ]:  No email set

Some users might still receive the email update, but when Confluence try to send an email to John Doe (who does not have an email) it will log the warning above and stop sending email.

Hence the rest of the recipients in the Confluence Changes in the last 24 Hours list will not receive the digest mail.