Bug found and fixed...

includes/modules/shipping/canadapost.php

replace line 165
if ($this->lettermail_available && ($shipping_weight <= $this->lettermail_max_weight))

with this:
// Twitch bugfix - add lettermail switch control
// orginal code if ($this->lettermail_available && ($shipping_weight <= $this->lettermail_max_weight))
if (MODULE_SHIPPING_CANADAPOST_LETTERMAIL_STATUS == 'True' && ($shipping_weight <= $this->lettermail_max_weight))


Enable Lettermail Rates switch will now function properly.


Remember this uses the Max weight for Lettermail and the table rate settings correctly and needs 0's as placeholders or you will get non-numeric errors in your log folder.