Magento event sales_order_invoice_register is called multiple times -

i'm trying observe event sales_order_invoice_register because need send custom emails once invoice created.

on of invoiced orders i've received email (sent observer) multiple times.

is possible register function mage_sales_model_order_invoice called multiple times same order has 1 invoice?

if sales_order_invoice_register not best event watch for, i'm open suggestions.

thank you.

braintree creating order & invoice on every credit card form submit if card details incorrect.

instead of sales_order_invoice_register i've changed observer use event sales_order_invoice_pay