This script:
$f=explode('@',$email);
$mxOK=getmxrr($f[1],$mxhosts,$mxweight);
$aOK=checkdnsrr($f[1],'A');
$aOK=$aOK or checkdnsrr($f[1],'CNAME');
works OK on Linux, but not working under NT
(always failed to get DNS records).

------- php.ini --------
[PHP_3]

;;;;;;;;;;;;;;;;;;;
; About this file ;
;;;;;;;;;;;;;;;;;;;
; This file controls many aspects of PHP's behavior.  In order for PHP to
; read it, it must be named 'php3.ini'.  PHP looks for it in the current
; working directory, in the path designated by the environment variable
; PHPRC, and in the path that was defined in compile time (in that order).
; Under Windows, the compile-time path is the Windows directory.  The
; path in which the php3.ini file is looked for can be overriden using
; the -c argument in command line mode.
;
; The syntax of the file is extremely simple.  Whitespace and Lines
; beginning with a semicolon are silently ignored (as you probably guessed).
; Section headers (e.g. [Foo]) are also silently ignored, even though
; they might mean something in the future (they probably won't).
;
; Options are specified using the syntax key = value or key = "complex value".
; Key names are *case sensitive*.  foo = bar is different from FOO = bar.
; 'value' can be any number, word or keyword (keywords are On, Off, True,
; False, Yes and No, and are case insensitive).
; 'complex value' can be just about anything, expcept for " and a newline
; Boolean flags can be turned on using the values 1, On, True or Yes.
; They can be turned off using the values 0, Off, False or No.
;
; All the values in the php3.ini-dist file correspond to the builtin
; defaults (that is, if no php3.ini is used, or if you delete these lines,
; the builtin defaults will be identical).


;;;;;;;;;;;;;;;;;;;;
; Language Options ;
;;;;;;;;;;;;;;;;;;;;

engine                  =       On      ; enable PHP 3.0 parser
short_open_tag  =       On      ; allow the <? tag.  otherwise, only <?php and <script> tags are recognized.
asp_tags                =       Off ; allow ASP-style <% %> tags
precision               =       14      ; number of significant digits displayed in floating point numbers
y2k_compliance  =       Off     ; whether to be year 2000 compliant (will cause problems with non y2k compliant browsers)
; Safe Mode
safe_mode               =       Off
safe_mode_exec_dir      =
; Colors for Syntax Highlighting mode.  Anything that's acceptable in <font color=???> would work.
highlight.string        =       #DD0000
highlight.comment       =       #FF8000
highlight.keyword       =       #007700
highlight.bg            =       #FFFFFF
highlight.default       =       #0000BB
highlight.html          =       #000000


;;;;;;;;;;;;;;;;;;;
; Resource Limits ;
;;;;;;;;;;;;;;;;;;;

max_execution_time = 30000     ; Maximum execution time of each script, in seconds
memory_limit = 8388608          ; Maximum amount of memory a script may consume (8MB)


;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Error handling and logging ;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; error_reporting is a bit-field.  Add each number up to get desired error reporting level
;  1 = Normal errors
;  2 = Normal warnings
;  4 = Parser errors
;  8 = Notices - warnings you can ignore, but sometimes imply a bug (e.g., using an uninitialized variable)
error_reporting =       7
display_errors  =       On      ; Print out errors (as a part of the HTML script)
log_errors              =       Off     ; Log errors into a log file (server-specific log, stderr, or error_log (below))
track_errors    =       Off     ; Store the last error/warning message in $php_errormsg (boolean)
;error_prepend_string = "<font color=ff0000>"   ; string to output before an error message
;error_append_string = "</font>"                ; string to output after an error message
;error_log      =       c:\php_error_log        ; log errors to specified file
;error_log      =       syslog          ; log errors to syslog (Event Log on NT, not valid in Windows 95)
warn_plus_overloading   =       Off             ; warn if the + operator is used with strings


;;;;;;;;;;;;;;;;;
; Data Handling ;
;;;;;;;;;;;;;;;;;
magic_quotes_gpc        =       On              ; magic quotes for incoming GET/POST/Cookie data
magic_quotes_runtime=   Off             ; magic quotes for runtime-generated data, e.g. data from SQL, from exec(), etc.
magic_quotes_sybase     =       Off             ; Use Sybase-style magic quotes (escape ' with '' instead of \')
track_vars                      =       On              ; enable $HTTP_GET_VARS[], $HTTP_POST_VARS[] and $HTTP_COOKIE_VARS[] arrays
; automatically add files before or after any PHP 3.0 document
auto_prepend_file       =
auto_append_file        =


;;;;;;;;;;;;;;;;;;;;;;;;;
; Paths and Directories ;
;;;;;;;;;;;;;;;;;;;;;;;;;
include_path    =                   ; UNIX: "/path1:/path2"  Windows: "\path1;\path2"
doc_root                =                                       ; the root of the php pages, used only if nonempty
user_dir                =                                       ; the directory under which php opens the script using /~username, used only if nonempty
;upload_tmp_dir =                       ; temporary directory for HTTP uploaded files (will use system default if not specified)
upload_max_filesize = 2097152       ; 2 Meg default limit on file uploads
extension_dir   =       e:\php3\                              ; directory in which the loadable extensions (modules) reside


;;;;;;;;;;;;;;;;;;;;;;
; Dynamic Extensions ;
;;;;;;;;;;;;;;;;;;;;;;
; if you wish to have an extension loaded automaticly, use the
; following syntax:  extension=modulename.extension
; for example, on windows,
; extension=msql.dll
; or under UNIX,
; extension=msql.so


;Windows Extensions
extension=php3_mysql.dll
extension=php3_nsmail.dll
;extension=php3_calendar.dll
;extension=php3_dbase.dll
;extension=php3_filepro.dll
;extension=php3_gd.dll
;extension=php3_dbm.dll
;extension=php3_mssql.dll
;extension=php3_zlib.dll
;extension=php3_filepro.dll
;extension=php3_imap4r2.dll
;extension=php3_ldap.dll
;extension=php3_crypt.dll
;extension=php3_msql2.dll
;extension=php3_odbc.dll

;;;;;;;;;;;;;;;;;;;
; Module Settings ;
;;;;;;;;;;;;;;;;;;;

[Syslog]
define_syslog_variables = Off   ; Whether or not to define the various syslog variables,
                                                                ; e.g. $LOG_PID, $LOG_CRON, etc.  Turning it off is a
                                                                ; good idea performance-wise.  In runtime, you can define
                                                                ; these variables by calling define_syslog_variables()


[mail function]
SMTP                    =       localhost                       ;for win32 only
sendmail_from   =       php3@forth.org.ru        ;for win32 only
sendmail_path   =                                               ;for unix only, may supply arguments as well (default is sendmail -t)

[Debugger]
debugger.host   =       localhost
debugger.port   =       7869
debugger.enabled        =       False

[Logging]
; These configuration directives are used by the example logging mechanism.
; See examples/README.logging for more explanation.
;logging.method    = db
;logging.directory = /path/to/log/directory

[SQL]
sql.safe_mode   =       Off

[ODBC]
;uodbc.default_db               =       Not yet implemented
;uodbc.default_user             =       Not yet implemented
;uodbc.default_pw               =       Not yet implemented
uodbc.allow_persistent  =       On      ; allow or prevent persistent links
uodbc.max_persistent    =       -1      ; maximum number of persistent links. -1 means no limit
uodbc.max_links                 =       -1      ; maximum number of links (persistent+non persistent). -1 means no limit
uodbc.defaultlrl        =       4096    ; Handling of LONG fields. Returns number of bytes to variables, 0 means passthru
uodbc.defaultbinmode    =       1       ; Handling of binary data. 0 means passthru, 1 return as is, 2 convert to char
; See the documentation on odbc_binmode and odbc_longreadlen for an explanation of uodbc.defaultlrl
; and uodbc.defaultbinmode

[MySQL]
mysql.allow_persistent  =       On      ; allow or prevent persistent link
mysql.max_persistent    =       -1      ; maximum number of persistent links. -1 means no limit
mysql.max_links                 =       -1      ; maximum number of links (persistent+non persistent).  -1 means no limit
mysql.default_port              =               ; default port number for mysql_connect().  If unset,
                                                                ; mysql_connect() will use the $MYSQL_TCP_PORT, or the mysql-tcp
                                                                ; entry in /etc/services, or the compile-time defined MYSQL_PORT
                                                                ; (in that order).  Win32 will only look at MYSQL_PORT.
mysql.default_host              =               ; default host for mysql_connect() (doesn't apply in safe mode)
mysql.default_user              =               ; default user for mysql_connect() (doesn't apply in safe mode)
mysql.default_password  =               ; default password for mysql_connect() (doesn't apply in safe mode)
                                                                ; Note that this is generally a *bad* idea to store passwords
                                                                ; in this file.  *Any* user with PHP access can run
                                                                ; 'echo cfg_get_var("mysql.default_password")' and reveal that
                                                                ; password!  And of course, any users with read access to this
                                                                ; file will be able to reveal the password as well.

[mSQL]
msql.allow_persistent   =       On      ; allow or prevent persistent link
msql.max_persistent             =       -1      ; maximum number of persistent links. -1 means no limit
msql.max_links                  =       -1      ; maximum number of links (persistent+non persistent).  -1 means no limit

[PostgresSQL]
pgsql.allow_persistent  =       On      ; allow or prevent persistent link
pgsql.max_persistent    =       -1      ; maximum number of persistent links. -1 means no limit
pgsql.max_links                 =       -1      ; maximum number of links (persistent+non persistent).  -1 means no limit

[Sybase]
sybase.allow_persistent =       On      ; allow or prevent persistent link
sybase.max_persistent   =       -1      ; maximum number of persistent links. -1 means no limit
sybase.max_links                =       -1      ; maximum number of links (persistent+non persistent).  -1 means no limit
;sybase.interface_file  =       "/usr/sybase/interfaces"
sybase.min_error_severity       =       10      ; minimum error severity to display
sybase.min_message_severity     =       10      ; minimum message severity to display
sybase.compatability_mode       = Off   ; compatability mode with earlier versions of PHP 3.0.
                                                                        ; If on, this will cause PHP to automatically assign types to results
                                                                        ; according to their Sybase type, instead of treating them all as
                                                                        ; strings.  This compatability mode will probably not stay around
                                                                        ; forever, so try applying whatever necessary changes to your code,
                                                                        ; and turn it off.

[Sybase-CT]
sybct.allow_persistent  =       On              ; allow or prevent persistent link
sybct.max_persistent    =       -1              ; maximum number of persistent links. -1 means no limit
sybct.max_links                 =       -1              ; maximum number of links (persistent+non persistent).  -1 means no limit
sybct.min_server_severity       =       10      ; minimum server message severity to display
sybct.min_client_severity       =       10      ; minimum client message severity to display

[bcmath]
bcmath.scale    =       0       ; number of decimal digits for all bcmath functions

[browscap]
;browscap       =       extra/browscap.ini

[Informix]
ifx.default_host                =               ; default host for ifx_connect() (doesn't apply in safe mode)
ifx.default_user                =               ; default user for ifx_connect() (doesn't apply in safe mode)
ifx.default_password            =               ; default password for ifx_connect() (doesn't apply in safe mode)
ifx.allow_persistent            =       On      ; allow or prevent persistent link
ifx.max_persistent              =       -1      ; maximum number of persistent links. -1 means no limit
ifx.max_links                   =       -1      ; maximum number of links (persistent+non persistent).  -1 means no limit
ifx.textasvarchar               =       0       ; if set on, select statements return the contents of a text blob instead of it's id
ifx.byteasvarchar               =       0       ; if set on, select statements return the contents of a byte blob instead of it's id
ifx.charasvarchar               =       0       ; trailing blanks are stripped from fixed-length char columns. May help the life
                                                ; of Informix SE users. 
ifx.blobinfile                  =       0       ; if set on, the contents of text&byte blobs are dumped to a file instead of
                                                ; keeping them in memory
ifx.nullformat                  =       0       ; NULL's are returned as empty strings, unless this is set to 1. In that case,
                                                ; NULL's are returned as string 'NULL'.