HS POP3 Library

HS POP3 is a reliable software library written in C that delivers the client-side implementation of Post Office Protocol Version 3 (POP3) over TCP socket layer in compliance with RFC 1939. It comes with a full source code and supports a variety of features including user authentication, text reception of basic internet headers, message deletion, and statistics.

One of the most noteworthy features of the HS POP3 is its support for secure POP3 over Transport Layer Security (TLS) and Secure Sockets Layer (SSL). It supports two methods, namely POP3S (used by Gmail) and RFC 2595. Furthermore, it has the ability to extract binary file attachments in MIME v1.0 base64 format.

The user application utilizes HS POP3 initialization function to supply pointers to callback functions in the user code for memory and timer management and for reporting POP3 events to the user. To obtain email messages from any POP3 RFC1939 compliant server, the user application calls HsPop3GetMail function by specifying the mail server name or IP address and login user name and password.

Once the library has already resolved the server name, it connects to it and starts the message scan list according to the RFC1939 standard. Since HS POP3 has a unique message ID from the server, it reports this message ID to the user application via a callback function. If the user code is interested in receiving the message, it will return a specific value. HS POP3 will then request the necessary memory amount and receive the complete message into the buffer.

When the message is received, the user code is notified by a callback and a message structure containing the pointer to the full message, its length, the start of text pointer, the length of headers, and separately parsed out header information, including the from field, date field, message ID field, and subject field. This process repeats until all messages are received. The HS POP3 library can also delete messages from the server if the user specifies this option.

In addition, HS POP3 boasts of a modular design that makes it easy to port its protocol module to any environment. Its internal lower layer interfaces with the HS Sock library, which provides TCP transport services. Overall, the HS POP3 offers a great combination of features and reliability, making it an excellent software library for POP3 implementations.