Samsung are a pain to setup email
For general use email is good, i use some to report network loss etc
Unlikely to be the email provider as you could use another DVR different make and it will always work , you probably have changed something and need to break it down as swb says
Recently when O2 and others were working on there network ipolis was not working or sometimes other functions would not work because of how Samsung drs work , following day back to normal