Ставил vtiger на FreeBSD.
При проверке системы выдает что
IMAP Support Availability   Failed. Not Available.
Так как под FreeBSD vtiger нет, посмотрел зависимости для Linux.
Вероятно это выдает сообщение из-за отстутсвия imap-2004d.
Нашел исходник imap-2004d.tar.Z
#tar -xzvf imap-2004d.tar.Z
#cd imap-2004d
#cat README
#cat README
                           IMAP Toolkit Environment
                              14 September 2004
                                 Mark Crispin

                            UNIX QUICK BUILD NOTES

These quick build notes assume that you have installed OpenSSL before
attempting to build this software, and that you do not have any non-default
configuration parameters.

If you need additional information in building this software with OpenSSL,
please refer to the docs/SSLBUILD file for more information.

If you intend to build this software with a non-default configuration
(including building a non-compliant server without SSL support), please
refer to the docs/BUILD file for more information.

1) Look in imap-2004/Makefile and find your system type code.  For example,
   modern versions of Linux will use either "slx", "lnp", or one of the
   lnp-variants (such as "lrh").

2) Type "make" followed by the system type, e.g. "make slx".

3) Install the POP2 daemon (ipopd/ipop2d), the POP3 daemon (ipopd/ipop3d), and
   the IMAP daemon (imapd/imapd) on a system directory of your choosing.

4) Update /etc/services to register the pop2 service on TCP port 109, the
   pop3 service on TCP port 110, and the imap service on TCP port 143.  Also
   update Yellow Pages/NIS/NetInfo/etc. if appropriate on your system.

5) Update /etc/inetd.conf to invoke the POP2, POP3, and IMAP daemons on their
   associated services.

6) That's all!

Read the file docs/BUILD if you need more detailed information and/or you
don't understand these quick build instructions.

                             MISCELLANEOUS NOTES

     mtest has been run under UNIX, DOS, Windows, NT, Macintosh, TOPS-20, and
VMS.  It is a very primitive interface, however, and is suited mainly as a
model of how to write a main program for c-client.  You should take a look at
the source to figure out how to use it.  Briefly, it first asks for a mailbox
name (either a local file path or an IMAP mailbox in the form
"{hostname}mailbox") and then puts you in a command mode where "?" will give
you a list of commands.

     Pine is available separately on the FTP.CAC.Washington.EDU archives.

     The focus of development and support is for UNIX and Win32 (including
Windows 95/98/Millenium, Windows NT, and Windows 2000).  The other ports are
not frequently used or tested, and may be incomplete.

#make bsf

в соответствии с README скопировал imapd в /usr/local/sbin
поправил inetd.conf
запустил inetd

Все равно выдало недосутпаность imapd.

ВОПРОС

В коде проверки нашел строку

php echo function_exists('imap_open')

посмотрел
function_exists

(PHP 3 >= 3.0.7, PHP 4, PHP 5)
function_exists --  Возвращает TRUE, если данная функция определена
Описание
bool function_exists ( string function_name )

Проверяет, есть ли в списке определённых функций, встроенных и пользовательских, функция function_name. Возвращает TRUE в случае успешного завершения или FALSE в случае возникновения ошибки.

где определить данную функцию и где она определяется?