(C) Yahoo! IMAP (imap.mail.yahoo.com)

(from Wikipedia)

It is possible to get direct IMAP access without signing up for paid access nor using software like YPOPs! or FreePOPs. Yahoo! operates IMAP and secure IMAP servers (imap.mail.yahoo.com in particular), which are globally accessible. However they require a specific, non-standard IMAP command to be sent before login is done, namely: “ID ("GUID" "1")”.

Chilkat C/C++ Library Downloads
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#include <C_CkImap.h>

void ChilkatSample(void)
    {
    HCkImap imap;
    BOOL success;
    const char *rawResponse;

    // This example assumes the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    imap = CkImap_Create();

    // Connect to they Yahoo! IMAP server.
    CkImap_putPort(imap,993);
    CkImap_putSsl(imap,TRUE);
    success = CkImap_Connect(imap,"imap.mail.yahoo.com");
    if (success != TRUE) {
        printf("%s\n",CkImap_lastErrorText(imap));
        CkImap_Dispose(imap);
        return;
    }

    // Send the non-standard ID command...

    rawResponse = CkImap_sendRawCommand(imap,"ID (\"GUID\" \"1\")");
    if (CkImap_getLastMethodSuccess(imap) != TRUE) {
        printf("%s\n",CkImap_lastErrorText(imap));
        CkImap_Dispose(imap);
        return;
    }

    // Login
    success = CkImap_Login(imap,"myLogin","myPassword");
    if (success != TRUE) {
        printf("%s\n",CkImap_lastErrorText(imap));
        CkImap_Dispose(imap);
        return;
    }

    printf("Login Success!\n");

    // Select an IMAP mailbox
    success = CkImap_SelectMailbox(imap,"Inbox");
    if (success != TRUE) {
        printf("%s\n",CkImap_lastErrorText(imap));
        CkImap_Dispose(imap);
        return;
    }

    // Continue with whatever you wish to do...
    // (see other examples..)

    // Disconnect from the IMAP server.
    success = CkImap_Disconnect(imap);


    CkImap_Dispose(imap);

    }