Determine if an email address is valid

When you write a page with ASP, if it involves sending a message, you will normally be asked to enter your email address. Wrong email address often brings a lot of unnecessary trouble, use the following function IsValidEmail can determine an email address is valid.
Function Source code:
<%
Function IsValidEmail (Email)
Validflag = False
If (email <> "") and (INSTR (1, email, "@") > 0) and (InStr (1, email, ".") > 0) Then
Atcount = 0
Specialflag = False
For atloop = 1 to Len (Email)
ATCHR = Mid (Email, Atloop, 1)
If ATCHR = "@" Then Atcount = atcount + 1
If (ATCHR >= Chr ()) and (ATCHR <= Chr ()) Then Specialflag = True
If (ATCHR = CHR ()) or (ATCHR = Chr) or (ATCHR >= (CHR)) 123 Then = True
If (ATCHR >= Chr ()) and (ATCHR <= Chr ()) Then Specialflag = True
If (ATCHR >= Chr ()) and (ATCHR <= Chr ()) Then Specialflag = True
Next
If (Atcount = 1) and (Specialflag = False) Then
Badflag = False
TAry1 = Split (Email, "@")
UserName = tAry1 (0)
DomainName = TAry1 (1)
If (UserName = "") Or (domainname = "") Then Badflag = True
If Mid (domainname, 1, 1) = "." Then Badflag = True
If Mid (domainname, Len (domainname), 1) = "." Then Badflag = True
Validflag = True
End If
End If
If Badflag = True Then Validflag = False
IsValidEmail = Validflag
End Function
%>
Use examples:
IsValidEmail (" my_263_email@263.net ") returns ture
IsValidEmail (" zh99wj@tonghua.com.cn ") returns ture
IsValidEmail ("Myemail263.net") returns false
IsValidEmail (" my_263_email@263 ) returns false
Note that the function simply determines whether the email address format is valid, but does not check that the address does exist.