More information in 'Failed' tag by e-mail tickets who don't reach customers inbox for some reason.
When an e-mail can not be delivered trengo tags the ticket with 'failed'. There is no information attatched about why the e-mail couldn't be delivered. Because of this, I have to contact support to see if they can fix it for us and re- sent the e-mail. This is far from ideal and could be resolved by sharing the reason why the e-mail does not reach the customers inbox.