rt-thread/components/net/uip/apps/smtp/smtp-strings

smtp_220 "220"
smtp_helo "HELO "
smtp_mail_from "MAIL FROM: "
smtp_rcpt_to "RCPT TO: "
smtp_data "DATA\r\n"
smtp_to "To: "
smtp_from "From: "
smtp_subject "Subject: "
smtp_quit "QUIT\r\n"
smtp_crnl "\r\n"
smtp_crnlperiodcrnl "\r\n.\r\n"