IMAP is used to receive and read e-mail, and SMTP is used to send it. SMTP setting depends on the e-mail service you are using, and sometimes your Internet provider.
If you are using an e-mail program like Thunderbird or Outlook, check how SMTP server is configured in that program. Otherwise, contact your e-mail provider or search the web for "SMTP <your e-mail supplier name>" for the correct settings.