These functions are not limited to the IMAP protocol, despite their name. The underlying c-client library also supports NNTP, POP3 and local mailbox access methods.
This extension requires the c-client library to be installed. Grab the latest version from ftp://ftp.cac.washington.edu/imap/ and compile it.
To get these functions to work, you have to compile PHP with --with-imap.
Then copy c-client/c-client.a to /usr/local/lib/libc-client.a or some other directory on your link path and copy c-client/c-client.h, c-client/imap4r1.h, c-client/rfc-882.h, c-client/mail.h and c-client/linkage.h to /usr/local/include or some other directory in your include path.
Note: Depending how the c-client was configured, you might also need to add --with-imap-ssl=/path/to/openssl/ and/or --with-kerberos into the PHP configure line.
The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.
This document can't go into detail on all the topics touched by the provided functions. Further information is provided by the documentation of the c-client library source (docs/internal.txt). and the following RFC documents:
RFC2821: Simple Mail Transfer Protocol (SMTP).
RFC2822: Standard for ARPA internet text messages.
RFC2060: Internet Message Access Protocol (IMAP) Version 4rev1.
RFC1939: Post Office Protocol Version 3 (POP3).
RFC977: Network News Transfer Protocol (NNTP).
RFC2076: Common Internet Message Headers.
Crashes and startup problems of PHP may be encountered when loading this extension in conjunction with the recode extension. See the recode extension for more information.