Using the Personal Dictionary
Postbox can learn the spelling of words that you type frequently, and un-learn words that have been learned by mistake.
Learning a New Word
Type the word you'd like Postbox to learn followed by the spacebar, so it becomes underlined in red. Then do a right-click (control-click on Mac) and select "Add to Dictionary."
Forgetting a Word
Here's how to remove a word from your personal dictionary:
1) Create a new message.
2) Click in the body of the message.
3) Go to Options > Check Spelling...
4) Click the Edit button under "Personal Dictionary"
5) Select the word you would like to remove.
6) Click Remove.