It was probably an automated mistake. When this happened to me, I logged directly into the mail account of the affected user to automatically remove the suspension.
http://mail.google.com/a/domain.com/ If this doesn't work, you can sign up for a free trial of Apps for Business to get support. You might have been suspended for quite some time already. App Engine only started alerting about this recently. https://code.google.com/p/googleappengine/issues/detail?id=6181 -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To unsubscribe from this group and stop receiving emails from it, send an email to google-appengine+unsubscr...@googlegroups.com. To post to this group, send email to google-appengine@googlegroups.com. Visit this group at http://groups.google.com/group/google-appengine?hl=en. For more options, visit https://groups.google.com/groups/opt_out.