Reproduced by me: mail server is configured correct and was unable to get blog comments to send notification to the blog writer.
1) Install liferay 6.0.4 bundle
2) Run, check server administration panel for portal properties "blogs.email.comments.added.enabled" and "message.boards.email.message.added.enabled" are set to true
3) Configure SMTP server (also in administration panel)
For easy SMTP temporary setup, use these settings with your Gmail account as the SMTP server:
SMTP Server: smtp.gmail.com
[x] Use Secure Connection
User: Your gmail username
Password: Your gmail password
4) Create a new administrator user. make sure the email address is one that you can receive email at.
5) confirm that you received a "new user account" email
6) and add a blog portlet in his account as well as a blog post.
7) Comment on it with email@example.com
8) It should send you an email that a comment was added, but it doesn't.
I'll add reproduce steps for the message board emails too if I can reproduce it