Most TCP ports are general-purpose channels that can be called into service as needed but otherwise sit idle. Some lower-numbered ports, however, are dedicated to specific applications. While many TCP ports belong to applications that no longer exist, certain ones are very popular. Jason Gillikin Jason Gillikin On the receiving end, port 110 governs Post Office Protocol, version 3, and port 143 is dedicated to Internet Mail Access Protocol. POP3 and IMAP control the flow of emails from your provider’s server to your inbox. The secure versions of SMTP and IMAP vary depending on configuration, but ports 465 and 587 are common. Port 443 is the default for secure HTTP. Unlike ports with lower numbers, developers of new TCP/UDP services can select a specific number to register with IANA rather than having a number assigned to them. Using registered ports also avoids the additional security restrictions that operating systems place on ports with lower numbers.
