You will have to talk to your network administrator to get this. In case you are using an external provider like godaddy, this information is available on various sites, including godaddy faqs/blogs - for example smtp server of godaddy is
relay-hosting.secureserver.net
.
Else, if you are just working on a private project, you can set up an smtp server for yourself by following instructions
here[
^],
here[
^] or
here[
^].