For smtp, the sendmail binary is started with the parameter -bs: Use the SMTP protocol on standard input and output. For pipe, the binary is started with the parameters -t: Read message from STDIN and extract recipients.
option
For smtp, the sendmail binary is started with the parameter -bs: Use the SMTP protocol on standard input and output. For pipe, the binary is started with the parameters -t: Read message from STDIN and extract recipients.