Validating email addresses using System.Text.RegularExpressions

[Doug]

I'm a little confused by this functionality. It doesn't seem to be
behaving like it should.

I am using the following regular expression to validate email
addresses:
"\w+([-+.]\w+)*@\w+([-.]\w+)*\.([a-zA-Z]{2,4})\040*". From what I can
determine it should validate the following rules:

1. BEFORE THE AMPERSAND
A. Must contain at least one alphanumeric character.
B. Can contain a '-', '+', or '.' character but if it does it
must have a alphanumeric character on either side of it.
2. AFTER THE AMPERSAND BUT BEFORE THE '.'
A. Must contain at least one alphanumeric character.
B. Can contain a '-', or '.' character but if it does it must
have a alphanumeric character on either side of it.
3. AFTER THE '.'
A. Must contain at least two alphabetical characters but no more
than 4.

However when I use System.Text.RegularExpressions.RegEx with this
expression and use the IsMatch method and use an email address like
dn******@dtgnet.com@dn******@dtgnet.com it returns true as if that was
a valid email address based on the rules.

Doesn't the {2,4} mean that it has to have a minimum of 2 characters
after the '.' character but no more than 4? Also, doesn't the
[a-zA-Z] mean that the characters after the '.' must be alphabetical
only? My tests seem to prove otherwise.

Any help on this would be great...thanks!

[Stoitcho Goutsev \(100\) [C# MVP]]

Hi Doug,

Here is the example in MSDN about validating email addresses

bool IsValidEmail(string strIn)
{
// Return true if strIn is in valid e-mail format.
return Regex.IsMatch(strIn,
@"^([\w-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([\w-]+\.)+))([a-zA
-Z]{2,4}|[0-9]{1,3})(\]?)$");
}
--
HTH
Stoitcho Goutsev (100) [C# MVP]
"Doug" <dn******@dtgnet.com> wrote in message
news:ff**************************@posting.google.c om...

I'm a little confused by this functionality. It doesn't seem to be
behaving like it should.

I am using the following regular expression to validate email
addresses:
"\w+([-+.]\w+)*@\w+([-.]\w+)*\.([a-zA-Z]{2,4})\040*". From what I can
determine it should validate the following rules:

1. BEFORE THE AMPERSAND
A. Must contain at least one alphanumeric character.
B. Can contain a '-', '+', or '.' character but if it does it
must have a alphanumeric character on either side of it.
2. AFTER THE AMPERSAND BUT BEFORE THE '.'
A. Must contain at least one alphanumeric character.
B. Can contain a '-', or '.' character but if it does it must
have a alphanumeric character on either side of it.
3. AFTER THE '.'
A. Must contain at least two alphabetical characters but no more
than 4.

However when I use System.Text.RegularExpressions.RegEx with this
expression and use the IsMatch method and use an email address like
dn******@dtgnet.com@dn******@dtgnet.com it returns true as if that was
a valid email address based on the rules.

Doesn't the {2,4} mean that it has to have a minimum of 2 characters
after the '.' character but no more than 4? Also, doesn't the
[a-zA-Z] mean that the characters after the '.' must be alphabetical
only? My tests seem to prove otherwise.

Any help on this would be great...thanks!

[Chris R. Timmons]

dn******@dtgnet.com (Doug) wrote in
news:ff**************************@posting.google.c om:

I'm a little confused by this functionality. It doesn't seem to
be behaving like it should.

I am using the following regular expression to validate email
addresses:
"\w+([-+.]\w+)*@\w+([-.]\w+)*\.([a-zA-Z]{2,4})\040*". From what
I can determine it should validate the following rules:

1. BEFORE THE AMPERSAND
A. Must contain at least one alphanumeric character.
B. Can contain a '-', '+', or '.' character but if it does
it
must have a alphanumeric character on either side of it.
2. AFTER THE AMPERSAND BUT BEFORE THE '.'
A. Must contain at least one alphanumeric character.
B. Can contain a '-', or '.' character but if it does it
must
have a alphanumeric character on either side of it.
3. AFTER THE '.'
A. Must contain at least two alphabetical characters but no
more
than 4.

However when I use System.Text.RegularExpressions.RegEx with
this expression and use the IsMatch method and use an email
address like dn******@dtgnet.com@dn******@dtgnet.com it returns
true as if that was a valid email address based on the rules.

Doesn't the {2,4} mean that it has to have a minimum of 2
characters after the '.' character but no more than 4? Also,
doesn't the [a-zA-Z] mean that the characters after the '.' must
be alphabetical only? My tests seem to prove otherwise.

Any help on this would be great...thanks!

Here's a method I use to validate e-mail addresses:

public static bool IsValidEmailAddress(string email)
{
if ((email != null) && (email.Trim().Length > 0))
{
return Regex.IsMatch(email, @"
^
[-a-zA-Z0-9][-.a-zA-Z0-9]*
@
[-.a-zA-Z0-9]+
(\.[-.a-zA-Z0-9]+)*
\.
(
com|edu|info|gov|int|mil|net|org|biz|
name|museum|coop|aero|pro
|
[a-zA-Z]{2}
)
$",
RegexOptions.IgnorePatternWhitespace);
}
else
{
return false;
}
}
You can find other regexes to validate e-mail addresses here:

http://regexlib.com/

--
Hope this helps.

Chris.
-------------
C.R. Timmons Consulting, Inc.
http://www.crtimmonsinc.com/