Provided by: libmail-checkuser-perl_1.24-2_all 
NAME
Mail::CheckUser - check email addresses for validity
SYNOPSIS
use Mail::CheckUser qw(check_email);
my $ok = check_email($email_addr);
use Mail::CheckUser qw(:constants check_email last_check)
my $ok = check_email($email_addr);
print "DNS timeout\n"
if last_check()->{code} == CU_DNS_TIMEOUT;
use Mail::CheckUser;
my $res = Mail::CheckUser::check_email($email_addr);
DESCRIPTION
This Perl module provides routines for checking validity of email address.
It makes several checks:
1. It checks the syntax of an email address.
2. It checks if there any MX records or A records for the domain part of the email
address.
3. It tries to connect to an email server directly via SMTP to check if mailbox is valid.
Old versions of this module performed this check via the VRFY command. Now the module
uses another check; it uses a combination of MAIL and RCPT commands which simulates
sending an email. It can detect bad mailboxes in many cases.
If is possible to turn off some or all networking checks (items 2 and 3). See "GLOBAL
VARIABLES".
This module was designed with CGIs (or any other dynamic Web content programmed with Perl)
in mind. Usually it is required to quickly check e-mail addresses in forms. If the check
can't be finished in reasonable time, the e-mail address should be treated as valid. This
is the default policy. By default if a timeout happens the result of the check is treated
as positive. This behavior can be overridden - see "GLOBAL VARIABLES".
IMPORTANT WARNING
In many cases there is no way to detect the validity of email addresses with network
checks. For example, non-monolithic mail servers (such as Postfix and qmail) often report
that a user exists even if it is not so. This is because in cases where the work of the
server is split among many components, the SMTP server may not know how to check for the
existence of a particular user. Systems like these will reject mail to unknown users, but
they do so after the SMTP conversation. In cases like these, the only absolutely sure way
to determine whether or not a user exists is to actually send a mail and wait to see if a
bounce messages comes back. Obviously, this is not a workable strategy for this module.
Does it mean that the network checks in this module are useless? No. For one thing, just
the DNS checks go a long way towards weeding out mistyped domain parts. Also, there are
still many SMTP servers that will reject a bad address during the SMTP conversation.
Because of this, it's still a useful part of checking for a valid email address. And this
module was designed such that if there is exists possibility (however small) that the
email address is valid, it will be treated as valid by this module.
Another warning is about $Mail::CheckUser::Treat_Timeout_As_Fail global variable. Use it
carefully - if it is set to true then some valid email addresses can be treated as bad
simply because an SMTP or DNS server responds slowly.
Another warning is about $Mail::CheckUser::Treat_Full_As_Fail global variable. Use it
carefully - if it is set to true then some valid email addresses can be treated as bad
simply because their mailbox happens to be temporarily full.
EXAMPLE
This simple script checks if email address "blabla@foo.bar" is valid.
use Mail::CheckUser qw(check_email last_check);
my $email = 'blabla@foo.bar';
if(check_email($email)) {
print "E-mail address <$email> is OK\n";
} else {
print "E-mail address <$email> isn't valid: ",
last_check()->{reason}, "\n";
}
SUBROUTINES
$ok = check_email($email)
Validates email address $email. Return true if email address is valid and false
otherwise.
$res = last_check()
Returns detailed result of last check made with "check_email" as hash reference:
{ ok => OK, code => CODE, reason => REASON }
OK True if last checked email address is valid. False otherwise.
CODE
A number which describes result of last check. See "CONSTANTS".
REASON
A string which describes result of last check.
CONSTANTS
Constants used by "last_check" to describe result of last check can be exported with
use Mail::CheckUser qw(:constants)
List of all defined constants:
CU_OK
Check is successful.
CU_BAD_SYNTAX
Bad syntax of email address.
CU_UNKNOWN_DOMAIN
Mail domain mentioned in email address is unknown.
CU_DNS_TIMEOUT
Timeout has happen during DNS checks.
CU_UNKNOWN_USER
User is unknown on SMTP server.
CU_SMTP_TIMEOUT
Timeout has happen during SMTP checks.
CU_SMTP_UNREACHABLE
All SMTP servers for mail domain were found unreachable during SMTP checks.
CU_MAILBOX_FULL
Mailbox is temporarily full but probably a valid username.
GLOBAL VARIABLES
It is possible to configure "check_email" using the global variables listed below.
$Mail::CheckUser::Skip_Network_Checks
If true then do only syntax checks. By default it is false.
$Mail::CheckUser::Skip_SMTP_Checks
If it is true then do not try to connect to mail server to check if a user exists. If
this is true, and $Mail::CheckUser::Skip_Network_Checks is false, only syntax and DNS
checks are performed. By default it is false.
$Mail::CheckUser::Skip_SYN
By default Net::Ping is used to determine remote reachability of SMTP servers before
doing SMTP checks. Setting this to true skips this check. By default it is false.
$Mail::CheckUser::Sender_Addr
MAIL/RCPT check needs an email address to use as the 'From' address when performing
its checks. The default value is "check@user.com".
$Mail::CheckUser::Helo_Domain
Sender domain used in HELO SMTP command. If undef Net::SMTP is allowed to use its
default value. By default it is undef.
Mail::CheckUser::Timeout
Timeout in seconds for network checks. By default it is 60.
$Mail::CheckUser::Treat_Timeout_As_Fail
If it is true "Mail::CheckUser" treats checks that time out as failed. By default it
is false.
$Mail::CheckUser::Treat_Full_As_Fail
If it is true "Mail::CheckUser" treats error "552 mailbox full" as an invalid email
and sets CU_MAILBOX_FULL. By default it is false.
$Mail::CheckUser::Treat_Grey_As_Fail
If it is true "Mail::CheckUser" treats all 400's errors as an invalid email and sets
CU_TRY_AGAIN. By default it is false.
$Mail::CheckUser::Net_DNS_Resolver
Override with customized Net::DNS::Resolver object. This is used to lookup MX and A
records for the email domain when network checks are enabled. If undef,
Net::DNS::Resolver->new will be used. The default value is undef.
$Mail::CheckUser::Debug
If it is true then enable debug output on "STDERR". By default it is false.
AUTHORS
Ilya Martynov ilya@martynov.org
Rob Brown bbb@cpan.org
Module maintained at Source Forge ( http://sourceforge.net/projects/mail-checkuser/ ).
COPYRIGHT
Copyright (c) 1999-2003 by Ilya Martynov. All rights reserved.
This program is free software; you can redistribute it and/or modify it under the same
terms as Perl itself.
$Id: CheckUser.pm,v 1.46 2003/09/18 23:51:36 hookbot Exp $
SEE ALSO
perl(1).