There are 17 words that start with 'postf'.
| postfix | postface | postfire | 
| postform | postfaces | postfault | 
| postfixal | postfixed | postfixes | 
| postforms | postfixing | postflight | 
| postformed | postfreeze | postforming | 
| postfeminist | postfracture | |
Note: These 17 words that start with 'postf' are found from the USA & Canada version of the tournament Scrabble word list.