exchange server send email issue

I can receive but not sent emails to my 1 and 1 exchange server. Some time ago my exchange email started playing up on my I phone, i don't use it often so i ignored it. Shortly after followed problems with my iPad and my mac. I talked to my service provider who could not fix my problem. My exchange server works perfectly on a PC and on Safari. The error message when I try to send mail says unexpected data.