I posted a while ago in Keeping your ear to the ground about searching the web for references to Esendex that might indicate someone having an issue.
I've got Google Alerts set up to track terms like 'Esendex Issue', 'Esendex Problem' and 'Esendex Delay'. One finally appeared.
Now the posts were from April last year but one of my support team went ahead and posted a reply anyway. Loh and behold the postee came straight back, happy. They were trialing at the time and had subsequently signed up as a customer.
I'm hoping that we're on top of it now and can react more quickly than over a year. If the customer hadn't been happy, they'd have been off and we'd never have known why.