You can make announcements to all the project users or send out a sticky or forum post for selected users. However, you can choose to be notified or not about these forums based on your preferred configuration for these notification mails in "Email Notification".
The notification mails for the forum posts are based on the forum type and their configured notifications as suggested:
I will walk you through some real-world scenarios on how the configured notification settings work for the different type of forum posts.
Email Notification
By default the option "Message Posted in Forums" is selected in the "Email Notification" tab in "Personal Settings". However, you can turn-off this option if you don’t wish to be notified about the forum posts in your portal.
1) I have disabled my notification preference for forums. Will I still receive a notification mail for forum announcement?
Any forum post made as an announcement is sent to all the portal users, regardless of their preference in "Email Notification" because announcements are supposed to reach all the users.
2) I have disabled my notification preference for forums. Will I still receive a notification mail for forums or sticky posts?
Condition
You are bombarded with a lot of notification mails, so you decide to disable any notifications w.r.t forums in "Email Notification".
How it works
What happens
You will receive a notification mail irrespective of whether you have disabled the "Message Posted in Forums" option or not because you are specifically tagged in the forum post. All the selected or tagged users will be notified.
3) I have enabled my notification preference for forums. Will I receive a notification mail for the sticky or forum post, though I am not a selected user?
Condition
You have selected your preference for forum notifications in "Email Notification" because you wish to be notified about all the forum posts, even if you are not mentioned or tagged.
How it works
What happens
You will still receive a notification mail because you have enabled the "Message Posted in Forums" option. However, it is not sent to users who have cleared this check box.
What is the difference between a forum post and sticky post?
Forums marked as sticky post is pinned at the top right inside forums as a point of reference for important posts, whereas forums are not pinned.