Get mail account from AD at MSSQL

1. Create the linked server
EXEC sp_addlinkedserver @server = 'ADSI',
                                           @srvproduct = 'Active Directory Services 2.5',
                                           @provider = 'ADSDSOObject',
                                           @datasrc = 'adsdatasource'

2. Security

3. SQL Function Script
ALTER FUNCTION [dbo].[GetEmailFromAD]
(
     -- Add the parameters for the function here
     @pUserID varchar(250)
)
RETURNS varchar(250)
AS
BEGIN
     -- Declare the return variable here
     DECLARE @pMail varchar(250)
     -- Add the T-SQL statements to compute the return value here
     SELECT @pMail = mail
     FROM OpenQuery (ADSI, '
                                      SELECT displayName,
                                      mail,
                                      sAMAccountName
                                      FROM ''LDAP://...:389/DC=...,DC=...,DC=...''
                                      WHERE objectCategory = ''User''
                                      ')
     WHERE sAMAccountName = RIGHT(@pUserID,LEN(@pUserID)-CHARINDEX('\',@pUserID))
     -- Return the result of the function
     RETURN @pMail
END