See [#6904] for back story.
Small change, but took a while to figure out what was going on (details in commit msg).
You can test by adding/removing user01 to/from the Post permission block list on a Tracker instance, and emailing comments thusly (make sure you have created a ticket):
swaks --server localhost:50088 --to email@example.com --from 'firstname.lastname@example.org' --body "test comment"
(You may need to yum install swaks.)
yum install swaks
Log in to post a comment.