If an anonymous user posts more than one comment using the same email BUT different case, comment_notify will send him more than one notify message.
I'll try to explain with an example:
- Anonymous 1 posts a comment using firstname.lastname@example.org as email
- when other users post comments, Anonymous 1 is correctly notified once for each comment
- Anonymous 1 posts another comment, now using Anonymous1@example.org as email (note the capital A)
- when other users post comments, Anonymous 1 is being notified twice: once at email@example.com and once at Anonymous1@example.org
_comment_notify_mailalert() function already contains a test to avoid multiple send to the same recipient, but this test is case-sensitive, so it does not work with my test case.