XLII. IMAP, POP3 and NNTP Functions
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.
It's important that you do not copy the IMAP source files directly into the system include directory as there may be conflicts. Instead, create a new directory inside the system include directory, such as /usr/local/imap-2000b/ (location and name depend on your setup and IMAP version), and inside this new directory create additional directories named lib/ and include/. From the c-client directory from your IMAP source tree, copy all the *.h files into include/ and all the *.c files into lib/. Additionally when you compiled IMAP, a file named c-client.a was created. Also put this in the lib/ directory but rename it as libc-client.a.
To get these functions to work, you have to compile PHP with --with-imap[=DIR], where DIR is the c-client install prefix. From our example above, you would use --with-imap=/usr/local/imap-2000b. This location depends on where you created this directory according to the description above. Windows users may include the php_imap.dll DLL in php.ini
由于这些常量是由该扩展模块定义的，因此只有在该扩展模块被编译到 PHP 中，或者在运行时被动态加载后，这些常量才有效。
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: