Well, I had a customer who paid me for a custom work around a month ago and I sent him the work the same day he made the payment. First time I tried to email him the work, the message returned back to me saying: This is an automatically generated Delivery Status Notification. Delivery to the following recipients failed. So, I sent the same email again and nothing returned back, so I was 100% sure he received it. Today, I received an email from him asking why I haven't sent him the work and I can't seem to reply.. I sent him numerous emails, some of them returned back to me, some didn't, but still no reply from him. I don't know any other emails of his and I've no idea what to do... He'll most likely open a Paypal dispute soon. The thing that annoys me the most is that I was able to send him emails before, but now I can't! Anyone has any ideas?
which mail service it is using (private or yahoo, gmail) it seems mx record problem if its on private domain than there is problem of his mx records you can show him the screen shots of the mails that you sent him and forward him the mails for failure