Can I set up 'Letter' rates at the checkout?

Yes, quoting letter rates is supported within Addition, you can activate 'Letter services' in a few steps.

One thing to note is that you are not able to create labels or fulfil letters online.  AustraliaPost do not support online lodgement when it comes to letters so you will need to drop letters into the nearest post shop.

Next steps:

• In the Rates section of the app, activate 'Retail', add services and select from the Letter options
• In the Packaging section of the app:
  • select 'Create Package'
  • select 'Retail' only
  • select 'Customer Checkout'
  • select 'Australia Post packaging' > the letter options will appear in the next drop down box below e.g.
    ​

If you are unfamiliar with the dimensions/weights of the Letter Services, here's Australia Post's official guide.

Domestic options within Addition:

1. Regular Small Letter 
2. Priority Small Letter 
3. Express Small Letter
4. Express Medium Letter
5. Regular Large Letter
6. Priority Large Letter 
7. Express Large Letter
8. Prepaid Regular DL Letter
9. Prepaid Priority DL Letter
10. Prepaid Registered Post DL Letter
11. Prepaid Regular C5 Letter 
12. Prepaid Priority C5 Letter 
13. Prepaid Regular Regular C4 Letter
14. Prepaid Priority C4 Letter 
15. Prepaid Regular B4 Letter
16. Prepaid Priority B4 Letter
17. Prepaid Registered Post B4 Letter 
18. Tracked DL Max Letter
19. Tracked C4 Letter

International options:

1. Economy Air Letter
2. Registered Post DL Letter 
3. Registered Post B4 Letter
4. Express Letter
5. Courier Letter