* Email Addresses
  * Keeping the ability to anonymously subscribe to a ticket is important; any validation?
  * Optional verification? This would require sending a message asking the person if they can receive mails, and until they say yes, never sending the notices. An external module to 'get' email would be required. 
  * Be sure apostrophes in names work okay.
  * ~~Should be able to plug-into an email address discovery system; e.g. if 'bob' is authenticated, get their address.~~
   * ~~It may be sufficient to add an '@address.com' to the end of an authenticated user in the case of an intranet, but not always. As figuring this out may be slightly complicated, the delivery system should perhaps allow a pluggable~~
  * Allow multiple email addresses per user? 
 * Delivery
  * Use a subprocess to prevent blocking and not require threads.
  * ~~Test plain text format mailing for proportional font~~ 
  * ~~Add some X-Trac-* headers for filtering perhaps?~~
  * ~~Email URL syntax: Ticket URL: <URL:http://developer.pidgin.im/ticket/1428#comment:2>~~
  * Allow for an email's Sender field to specify the user who made the change?
  * A /usr/bin/sendmail IAnnouncementDelivererererer module.
 * Tickets
  * Change notices should use the label, not the field name, for custom fields. 
  * trac:6306
  * Per-ticket watching beyond the subscription rule-system; e.g. in the ticket view one can click "Watch Me" with various options. "New comments", "status changed"... etc. 
  * Send notification when a file is attached?
   * Include link to the attachment.
  * Filter not just on 'prop changed', but on /certain/ props. Perhaps, "all, changed=field"
  * Filter on component owner.
  * Filter on "changed by..." E.g., self, vs others.
  * A "trivial change" notice? Let users filter on "non-trivial"
 * A Mailing List-type subscription? E.g., a list of users can receive a message on a new release? Notably would require an IMilestoneChangeListener. 
 * Wiki
  * Notify on change, delete, (rename?)
  * Notify on attachment add
 * Milestone
  * Notification on set-date, change-text, completion
 * Preference UI
  * Consider tile the preference boxes after a certain threshold of boxes are available.
Consider trac:5670 -- ???