<page_title> List of TCP and UDP port numbers </page_title> <section_title> Well-known ports </section_title> <table> <cell> 25 <col_header> Port </col_header> </cell> <cell> Yes <col_header> TCP </col_header> </cell> <cell> Simple Mail Transfer Protocol (SMTP), used for email routing between mail servers <col_header> Description </col_header> </cell> </table>
A TCP connection is on the "well-known port" for SMTP: port 25.