E-mail problems

I am new to the community, and my problem is that I can not send e-mails anymore. It has worked fine before but now I can not send even the simplest of e-mails.  The Norton Internet security box opens after I try to send an e-mail and says that 'the connection to the mail server has been interrupted. Go to "sent messages" file and try resending.'  Well, that used to work too, but it does not now! Any advice?

bill48