A comparative study of Simple Mail Transfer Protocol (SMTP), Post Office Protocol (POP) and X.400 Electronic Mail Protocols

We present the main features and functionality of the three most widely used message transfer protocols. We study actual implementations and base our analysis on benchmarking. The performance of the protocols is compared in terms of end to end delay, volume of traffic and number of frames generated at the physical layer and frame length distribution. An analytical model is proposed for the approximation of the upper and lower bounds of volume generated by SMTP which can easily be extended for POP3. The model considers both explicit and piggyback acknowledgements at the TCP layer.