I cannot get any new emails. I box states "I am disconnected". What do I do?

For several days I cannot get any new emails. A box comes up at the right bottom of the screen and says -- "Server _____________________________has disconnected. The server may have gone down or there may be a network problem." Also when I try to send emails a box comes up and says -- "Sending of message failed. The message could not be sent because the connection to SMTP server smtp.atlanticbb.net timed out. Try again or contact your network administrator." Please guide me how to fix this issue. Thank you in advance for all your help.