How to capture network traffic with tethereal

To capture and display all incoming SMTP rcpt to commands (where 1.2.3.4 is your IP address):

tethereal -d tcp.port==25,smtp -R "smtp and tcp.port == 25 and ip.dst == 1.2.3.4 and smtp.req.command == RCPT"

To capture and display all incoming rcpt to commands from specific ip (and where 1.2.3.4 is your IP address):

tethereal -d tcp.port==25,smtp -R "smtp and tcp.port == 25 and ip.dst == 1.2.3.4 and smtp.req.command == RCPT and ip.src == 5.6.7.8"