text: what to do if my mails from mail server to hotmail server are bouncing back as undelivered mail ?   bounce back is caused when the recipient have some problem with receiving mails. if u send mails to anyone and his/her mail box is full then there will be a bounce back to ur mailbox. if u r getting the bounce back then the person u r sending mails is having some inbox problem like space.... just say him/her to delete extra mails and free sum space for receiving incoming mails. also if the address u r sending mails does not exist, will cause a bounce back to your mailbox..