Or are they automatically deleted?

Go to account manager, click on 'My Board Posts'.  I don't know how far back it will show your posts, but you can see a lot of them.

Swim

The "view my post feature" only goes back 30 days.

However, if you go to the search messages tab on your local board, then type in your handle in the author box, you can search as far back as you want to go by using the day range.