hi annie ha, at first, you should know what kind of mail server you using. if your server using SMTP, than you can use our themes build in SMTP setting. but if you not using SMTP, you can disable it.
please note that every mail server having different setting. you may also need to configure your server MX – Record. the first think you should ask how to configure email on your server. or if they having support for setting up mx record, you should ask their support about this.