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**Joe Byrne** · 7 Dec 2007, 01:34 PM

Kev,

About 4 years ago I wrote a small program to validate the legitimacy of an EMail address. The idea was to see if the recipient's email server rejected the incoming email (mostly for unknown address errors). It worked pretty good, but I never fully developed it. I'm sure I have the source around here someplace, but it may take a while to search through my achieves.

The main idea though was pretty easy. Get the domain name from the email address. Open a normal SMTP session using the domain name, and follow the commands just as if you were an SMTP server. I gleaned most of my responses by simply getting the replies of the receiving server and logging what my SMTP servers were sending.

One of the best EMail server packages I've seen in a long time is hMailServer which is open source. You can install this, turn the logs on, and get all the handshake info you need.

In the mean time though, I'll see if I can't dig up my code for you.

**Joe Byrne** · 7 Dec 2007, 10:53 PM

Kev,

Well, I've located bits and pieces of the code but not the whole program itself. From what I remember though, the process went like this:

Strip off the domain name from the email address.
Get the 'A' record and all 'MX' records for the domain name
Make a direct connection to the domain using the 'A' and/or 'MX' records
Various tests, sending, etc.

The "hard" part was getting the MX records. You can get the 'A' record easily enough with

Code:

HOST ADDR Domain TO ARec&

The relevant code for getting the default DNS server address and MX records(which I got from here, I believe it is Borge's code) looks like this:

Code:

#INCLUDE "WSOCK32.INC"

%MAX_HOSTNAME_LEN = 128
%MAX_DOMAIN_NAME_LEN = 128
%MAX_SCOPE_ID_LEN = 256
'
TYPE FIXED_INFO
    HostName(%MAX_HOSTNAME_LEN + 4 - 1)AS BYTE
    DomainName(%MAX_DOMAIN_NAME_LEN + 4 - 1) AS BYTE
    CurrentDnsServer AS LONG
    DnsServerList    AS IP_ADDR_STRING
    NodeType         AS LONG
    ScopeId(%MAX_SCOPE_ID_LEN + 4 - 1) AS BYTE
    EnableRouting    AS LONG
    EnableProxy      AS LONG
    EnableDns        AS LONG
END TYPE
' Declare is done in a manner where we can use loadlibrary in case
' PC does not have iphlpapi.dll on it (like old Win 95 systems don't).
'
DECLARE FUNCTION GetNetworkParams ALIAS "GetNetworkParams" (BYREF pFixedInfo AS ANY, BYREF pOutBufLen AS LONG) AS LONG
'
'
%ERROR_NOT_SUPPORTED = 50
%ERROR_BUFFER_OVERFLOW = 111
%ERROR_INVALID_PARAMETER = 87
%ERROR_NO_DATA = 232
'******************************************


'****** DNS/MX Lookup Parameters *******
DECLARE FUNCTION GetMXName(dnsReply() AS BYTE, iNdx AS INTEGER, _ 
                 iAnCount AS INTEGER) AS STRING
DECLARE FUNCTION MX_Query(MailDomain AS STRING, DNSServer AS STRING) AS STRING
DECLARE SUB ParseName(dnsReply() AS BYTE, iNdx AS INTEGER, sName AS STRING)

%WINAPI               = 1
%WSABASEERR           = 10000
%WSAEINTR             = 10004
%WSAEBADF             = 10009
%WSAEACCES            = 10013
%WSAEFAULT            = 10014
%WSAEINVAL            = 10022
%WSAEMFILE            = 10024
%WSAEWOULDBLOCK       = 10035
%WSAEINPROGRESS       = 10036
%WSAEALREADY          = 10037
%WSAENOTSOCK          = 10038
%WSAEDESTADDRREQ      = 10039
%WSAEMSGSIZE          = 10040
%WSAEPROTOTYPE        = 10041
%WSAENOPROTOOPT       = 10042
%WSAEPROTONOSUPPORT   = 10043
%WSAESOCKTNOSUPPORT   = 10044
%WSAEOPNOTSUPP        = 10045
%WSAEPFNOSUPPORT      = 10046
%WSAEAFNOSUPPORT      = 10047
%WSAEADDRINUSE        = 10048
%WSAEADDRNOTAVAIL     = 10049
%WSAENETDOWN          = 10050
%WSAENETUNREACH       = 10051
%WSAENETRESET         = 10052
%WSAECONNABORTED      = 10053
%WSAECONNRESET        = 10054
%WSAENOBUFS           = 10055
%WSAEISCONN           = 10056
%WSAENOTCONN          = 10057
%WSAESHUTDOWN         = 10058
%WSAETOOMANYREFS      = 10059
%WSAETIMEDOUT         = 10060
%WSAECONNREFUSED      = 10061
%WSAELOOP             = 10062
%WSAENAMETOOLONG      = 10063
%WSAEHOSTDOWN         = 10064
%WSAEHOSTUNREACH      = 10065
%WSAENOTEMPTY         = 10066
%WSAEPROCLIM          = 10067
%WSAEUSERS            = 10068
%WSAEDQUOT            = 10069
%WSAESTALE            = 10070
%WSAEREMOTE           = 10071
%WSASYSNOTREADY       = 10091
%WSAVERNOTSUPPORTED   = 10092
%WSANOTINITIALISED    = 10093
%WSAEDISCON           = 10101
%WSAHOST_NOT_FOUND    = 11001
%WSATRY_AGAIN         = 11002
%WSANO_RECOVERY       = 11003
%WSANO_DATA           = 11004
%CLASS_IN             = 1       'Internet class
%QUERY_A              = 1       'Host Address
%QUERY_NS             = 2       'Authoritative Name Server
%QUERY_MD             = 3       'Mail destination (obsolete)
%QUERY_MF             = 4       'Mail Forwarder (Obsolete)
%QUERY_CNAME          = 5       'Canonical name of an alias
%QUERY_SOA            = 6       'Start Zone of Authority
%QUERY_MB             = 7       'Mailbox Domain Name
%QUERY_MG             = 8       'Mail Group Member
%QUERY_MR             = 9       'Mail Rename Domain Name
%QUERY_NULL           = 10      'Null resource record
%QUERY_WKS            = 11      'Well Known Service description
%QUERY_PTR            = 12      'Domain Name Pointer
%QUERY_HINFO          = 13      'Host Information
%QUERY_MINFO          = 14      'Mailbox or Mail List information
%QUERY_MX             = 15      'Mail Exchange
%QUERY_TXT            = 16      'Text
%QUERY_RP             = 17      'Responsible Person
%QUERY_AFSDB          = 18      'AFS Data Base Location
%QUERY_X25            = 19      'X.25 PSDN Address
%QUERY_ISDN           = 20      'ISDN Address
%QUERY_RT             = 21      'Route Through
%QUERY_NSAP           = 22      'NSAP Style A Record
%QUERY_NSAP_PTR       = 23      'NSAP Style A Record pointer
%QUERY_SIG            = 24      'Security Signature
%QUERY_KEY            = 25      'Security Key
%QUERY_PX             = 26      'X.400 Mail Mapping Information
%QUERY_GPOS           = 27      'Geographical Position
%QUERY_AAAA           = 28      'IP6 Address
%QUERY_LOC            = 29      'Location Information
%QUERY_NXT            = 30      'Next Domain
%QUERY_EID            = 31      'Endpoint Identifier
%QUERY_NIMLOC         = 32      'Nimrod Locator
%QUERY_SRV            = 33      'Server Selection
%QUERY_IXFR           = 251     'Incremental Transfer
%QUERY_AXFR           = 252     'Entire zone transfer
%QUERY_MAILB          = 253     'Mailbox-related RRs (MB, MG, or MR)
%QUERY_MAILA          = 254     'Mail Agent (obsolete)
%QUERY_ALL            = 255     'All Records
%ERROR_NOERROR        = 0        ' No Error
%ERROR_FORMAT         = 1        ' Format Error
%ERROR_SERVFAIL       = 2        ' Server Failure
%ERROR_NXDOMAIN       = 3        ' Non-Existent Domain
%ERROR_NOTIMP         = 4        ' Not Implemented
%ERROR_REFUSED        = 5        ' Query Refused
%ERROR_YXDOMAIN       = 6        ' Name Exists when it should not
%ERROR_YXRRSET        = 7        ' RR Set Exists when it should not
%ERROR_NXRRSET        = 8        ' RR Set that should exists does not
%ERROR_NOTAUTH        = 9        ' Server Not Authoritative for Zone
%DNS_FLAG_QR          = &H8000?
%DNS_FLAG_AA          = &H0800?
%DNS_FLAG_TC          = &H0400?
%DNS_RFLAG            = &H0100?
%DNS_FLAG_RA          = &H0100?
%DNS_RCODE_MASK       = &H000F?
%DNS_OPCODE_MASK      = &H7800?
%PACKETSZ             = 512' maximum packet size
%MAXDNAME             = 1025 ' maximum presentation domain name
%MAXCDNAME            = 255' maximum compressed domain name
%MAXLABEL             = 63 ' maximum length OF domain label
%HFIXEDSZ             = 12 ' bytes OF fixed data in header
%QFIXEDSZ             = 4  ' bytes OF fixed data in query
%RRFIXEDSZ            = 10 ' bytes OF fixed data in r record
%INADDRSZ             = 4  ' IPv4
%IN6ADDRSZ            = 16 ' IPv6 T_AAAA
%MAXALIASES           = 35
%MAXADDRS             = 35
%MAXDOMAINS           = 35
%MAXSERVERS           = 10
'User returned error codes
%ERROR_USER_NOERROR   =  0        ' No Error or empty query
%ERROR_USER_FORMAT    = -9        ' Format Error
%ERROR_USER_SERVFAIL  = -8        ' Server Failure
%ERROR_USER_NXDOMAIN  = -7        ' Non-Existent Domain
%ERROR_USER_NOTIMP    = -6        ' Not Implemented
%ERROR_USER_REFUSED   = -5        ' Query Refused
%ERROR_USER_YXDOMAIN  = -4        ' Name Exists when it should not
%ERROR_USER_YXRRSET   = -3        ' RR Set Exists when it should not
%ERROR_USER_NXRRSET   = -2        ' RR Set that should exists does not
%ERROR_USER_NOTAUTH   = -1        ' Server Not Authoritative for Zone
%ERROR_USER_NOQUERY   = -10       ' Query length passed is null or not a query


TYPE MX_RECORD
    wPreference AS WORD
    szName AS ASCIIZ * 256
    szDomain AS ASCIIZ * 256
    szIp AS ASCIIZ * 16
END TYPE

TYPE NS_RECORD
    szName AS ASCIIZ * 256
    szDomain AS ASCIIZ * 256
END TYPE

TYPE QR_REC
    wQueryType AS WORD
    wQueryClass AS WORD
END TYPE

TYPE DNS_HEADER
    wId AS WORD
    wBitFields AS WORD
    wQCount AS WORD
    wARCount AS WORD
    wAAcount AS WORD
    wAAARCount AS WORD
END TYPE

TYPE DNS_RR_HEADER
    wType AS WORD  'Type code (A, MX, etc)
    wClass AS WORD 'Class code (IN for internet, etc)
    dwTTL AS DWORD   'Time to live
    wLength AS WORD'Len of wRdata field (in octects)
    dwRData AS DWORD 'Field name address (variable length)
END TYPE

TYPE T_QUERY
    tHeader AS DNS_HEADER
    tQrRec AS QR_REC
END TYPE

UNION U_PARSE_PTR
    bPtr AS BYTE PTR
    wPtr AS WORD PTR
    lPtr AS LONG PTR
    dwPtr AS DWORD PTR
END UNION

TYPE sockaddralt
    sin_family AS INTEGER
    sin_port AS INTEGER
    sin_addr AS LONG
    sin_zero AS STRING * 8
END TYPE


FUNCTION DefaultDNS() AS STRING
    LOCAL lngFixedInfoNeeded    AS LONG
    LOCAL bytFixedInfoBuffer()  AS BYTE
    LOCAL udtFixedInfo          AS FIXED_INFO
    LOCAL Buffer                AS IP_ADDR_STRING
    LOCAL strFixedInfoScopeId   AS STRING
    LOCAL lngWin32apiResultCode AS LONG
    LOCAL ProcessID             AS LONG
    LOCAL hLib                  AS LONG
    LOCAL ProcAddr              AS DWORD
    LOCAL pAddrStr              AS LONG
    LOCAL I                     AS INTEGER
    
    ' Here we see if iphlpapi.dll is on this machine
    ProcessID = GETCURRENTPROCESSID()
    hLib = LOADLIBRARY("iphlpapi.dll")
    IF ISFALSE hLib THEN
       MSGBOX "Sorry, iphlpapi.dll not supported on this machine. Terminating program."
       EXIT FUNCTION
    END IF

    'Retrieve FUNCTION address
    ProcAddr = GETPROCADDRESS(hLib,"GetNetworkParams")
    IF ProcAddr = %NULL THEN
       MSGBOX "Sorry, GetNetworkParams not supported on this machine. Terminating program."
       EXIT FUNCTION
    END IF
    lngFixedInfoNeeded=LEN(udtFixedInfo)

    'Call pointer to the function using function prototype
    CALL DWORD ProcAddr USING GetNetworkParams(BYVAL %NULL ,lngFixedInfoNeeded) TO lngWin32apiResultCode
    IF lngWin32apiResultCode <> 0 THEN
       SELECT CASE lngWin32apiResultCode
            CASE %ERROR_BUFFER_OVERFLOW
                ' Right-size bytFixedInfoBuffer
                REDIM bytFixedInfoBuffer (lngFixedInfoNeeded)
            CASE %ERROR_INVALID_PARAMETER
                MSGBOX "Invalid parameter Error."
                EXIT FUNCTION
            CASE %ERROR_NO_DATA
                MSGBOX "No data Error."
                EXIT FUNCTION
            CASE %ERROR_NOT_SUPPORTED
                MSGBOX "Not Supported Error."
                EXIT FUNCTION
            CASE ELSE
                MSGBOX STR$(lngWin32apiResultCode) + " error code returned."
                EXIT FUNCTION
       END SELECT
    ELSE
       ' Something is horribly wrong as we should not get 0
       ' for the first pass through. Get outta here!
       MSGBOX "Unexpected result. Terminating program."
       EXIT FUNCTION
    END IF
    'Call pointer to the function using function prototype
    CALL DWORD ProcAddr USING GetNetworkParams(bytFixedInfoBuffer(0) , lngFixedInfoNeeded) TO lngWin32apiResultCode
    MOVEMEMORY bva(udtFixedInfo), bva(bytFixedInfoBuffer(0)), LEN(udtFixedInfo)
    
    FUNCTION = udtFixedInfo.DnsServerList.IpAddress
END FUNCTION


DNS$ = DefaultDNS

'---Look up MX record, check all 3 DNS services as needed---
FOR iLOOP& = 1 TO 3
    x$ = "NS" & FORMAT$(iLoop&)
    MX$ = TRIM$(MX_Query(Domain,DNS$))
    '---Sort any MX records returned by priority value---
    ARRAY SORT AllMXs(), FROM 1 TO 3
    iCount& = UBOUND(AllMXs())
    IF iCount& > 0 THEN EXIT FOR   'No need to test other DNS servers
    EZ_DOEVENTS 255
NEXT

MSGBOX FORMAT$(iCount&) & " MX records found"

FUNCTION MX_Query(MailDomain AS STRING, DNSServer AS STRING) AS STRING
    DIM StartupData AS WSAdata
    DIM SocketBuffer AS sockaddralt
    DIM IpAddr AS LONG
    DIM iRC AS INTEGER
    DIM dnsHead AS DNS_HEADER
    DIM iSock AS INTEGER
    DIM MailDomainTemp AS STRING
    DIM dnsQuery() AS BYTE
    DIM sQName AS STRING
    DIM dnsQueryNdx AS INTEGER
    DIM iTemp AS INTEGER
    DIM iNdx AS INTEGER
    DIM dnsReply(2048) AS BYTE
    DIM iAnCount AS INTEGER
    DIM I AS INTEGER
    DIM TempBuffer AS ASCIIZ*2049
    
    MailDomainTemp=TRIM$(MailDomain)
    ' Initialize the Winsocket
    iRC = WSAStartup(&H101, StartupData)
    FUNCTION=""
    ' Create a socket
    iSock = socket(%AF_INET, %SOCK_DGRAM, 0)
    IF iSock = %SOCKET_ERROR THEN EXIT FUNCTION
    HOST ADDR DNSServer TO IpAddr
    IF IpAddr = -1 THEN EXIT FUNCTION
    ' Setup the connnection parameters
    SocketBuffer.sin_family = %AF_INET
    SocketBuffer.sin_port = htons(53)
    SocketBuffer.sin_addr = IpAddr
    SocketBuffer.sin_zero = STRING$(8, 0)
    ' Set the DNS parameters
    dnsHead.wId = htons(&H11DF)            ' dnsHead.qryID = htons(&H11DF)
    dnsHead.wBitFields = 1                 ' dnsHead.options = DNS_RECURSION
    dnsHead.wQCount = htons(1)             ' dnsHead.qdcount = htons(1)
    dnsHead.wARCount = 0                   ' dnsHead.ancount = 0
    dnsHead.wAAcount = 0                   ' dnsHead.nscount = 0
    dnsHead.wAAARCount = 0                 ' dnsHead.arcount = 0 
    dnsQueryNdx = 0
    REDIM dnsQuery(4000)
    MOVEMEMORY BYVAL VARPTR(dnsQuery(dnsQueryNdx)), BYVAL VARPTR(dnsHead), 12
    dnsQueryNdx = dnsQueryNdx + 12
    sQName = MakeQName(MailDomainTemp)
    iNdx = 0
    WHILE (iNdx < LEN(sQName))
        dnsQuery(dnsQueryNdx + iNdx) = ASC(MID$(sQName, iNdx + 1, 1))
        iNdx = iNdx + 1
    WEND
    dnsQueryNdx = dnsQueryNdx + LEN(sQName)
    dnsQuery(dnsQueryNdx) = &H0
    dnsQueryNdx = dnsQueryNdx + 1
    iTemp = htons(15)
    MOVEMEMORY bva(dnsQuery(dnsQueryNdx)), bva(iTemp), LEN(iTemp)
    dnsQueryNdx = dnsQueryNdx + LEN(iTemp)
    iTemp = htons(1)
    MOVEMEMORY bva(dnsQuery(dnsQueryNdx)), bva(iTemp), LEN(iTemp)
    dnsQueryNdx = dnsQueryNdx + LEN(iTemp)
    REDIM PRESERVE dnsQuery(dnsQueryNdx - 1)
    iRC = sendto(iSock, dnsQuery(0), dnsQueryNdx + 1, 0, SocketBuffer, LEN(SocketBuffer))
    IF (iRC = %SOCKET_ERROR) THEN
        EXIT FUNCTION
    END IF
    iRC = recvfrom(iSock, dnsReply(0), 2048, 0, SocketBuffer, LEN(SocketBuffer))
    IF (iRC = %SOCKET_ERROR) THEN
        EXIT FUNCTION
    END IF
    MOVEMEMORY bva(iAnCount), bva(dnsReply(6)), 2
    iAnCount = ntohs(iAnCount)
    FOR I= 0 TO 2048
        TempBuffer=TempBuffer+CHR$(dnsReply(I))
    NEXT I
    FUNCTION = GetMXName(dnsReply(), 12, iAnCount)
END FUNCTION

That should be enough to at least get you in the right area. Let me know if you need more explaination.

**Knuth Konrad** · 8 Dec 2007, 07:23 AM

Originally posted by Kev Peel View Post

I'm having trouble finding a reliable third-party SMTP server that doesn't cost a bomb [...]

I'm using CMailServer whenever I'm in need of an easy to set up mailserver (i.e. for testing/demonstration purposes).

It's free for 5 users (5 mail accounts), which should be enough for your needs (just sending out emails, if I read your posting right).

**Kev Peel** · 8 Dec 2007, 09:21 AM

Thanks Joe & Knuth,

Joe that code looks especially useful

I'll also take a look at CMailServer.

The mailing lists may get very large in time as I will be adding the opt-in to my product pages and downloads sometimes hit >100 a day, so it would also be nice to detect and remove bad addresses from the lists and build a more "interactive" user-base. Mailings would only be sent when the product the list is related to is updated.

Thanks again!

**Martin Draper** · 9 Dec 2007, 07:17 PM

All the code for a full email server is in this forum. I know, I wrote it. The prototype uses a mysql backend but is a simple matter to use the alternate backend Sqlite the libraries for both have been posted. If you have any question please feel free

**Michael Burns** · 17 Dec 2007, 03:59 PM

The "hard" part was getting the MX records...

Florent Heyworth posted source code for MX record lookups a long time ago

Query DNS for MX (Mail Exchange) records - PowerBASIC Peer Support Community

http://www.powerbasic.com/support/pbforums/showthread.php?t=24950

PowerBASIC and related source code. Please do not post questions or discussions, just source code.

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