This installation documentation is based on RHEL or Centos based server. If you have debian or BSD , you need to install the proper c-client binary.
# yum install libc-client libc-client-devel krb5-devel krb5-libs
Now edit the file /usr/local/directadmin/custombuild/configure/ap2/configure.php5 and add the following two lines.
Now build the php using the following
# ./build php 5
After the compilation check the phpimap support using a phpinfo page
# php -m | grep imap
It is the easy way to install php-imap in directadmin server
PS: If you have 64 bit server make sure to enable a soft link as follows
# # ln -s /usr/lib64/libc-client.a /usr/lib/libc-client.a