Hi ,
I want to develop a solution in which all of the mails with attachment
will undergo a minor change i.e i will add some kind of watermarking.
For that i want to develop some kind of smtp proxy server which will
do the work of watermarking , further it will forward the mail to
actual smtp server.
Any pointers related to development of proxy server would be really
helpful.
Rgds,
Raan
Raan wrote:
> Hi ,
>
> I want to develop a solution in which all of the mails with attachment
> will undergo a minor change i.e i will add some kind of watermarking.
>
> For that i want to develop some kind of smtp proxy server which will
> do the work of watermarking , further it will forward the mail to
> actual smtp server.
>
> Any pointers related to development of proxy server would be really
> helpful.
Won't mimedefang/milter be a solution for this?
--
//Aho
In article <1193976408.215518.316420@v29g2000prd.googlegroups.com>,
Raan
> Hi ,
>
> I want to develop a solution in which all of the mails with attachment
> will undergo a minor change i.e i will add some kind of watermarking.
>
> For that i want to develop some kind of smtp proxy server which will
> do the work of watermarking , further it will forward the mail to
> actual smtp server.
>
> Any pointers related to development of proxy server would be really
> helpful.
I suggest that you don't do this, particularly if you are desperate
enough for clues on how to proceed that you are asking here. A lot of
people have written tools to do this sort of thing, and a very large
fraction of them have been done quite badly. There are significant
subtleties with an MTA making changes to a message body, and doing it in
the safest possible way is not always simple.
Instead, I suggest that you look at MIMEDefang
(http://www.mimedefang.org) which is a free "Milter" program that can do
exactly what you describe except that it does so as a plug-in to
Sendmail or Postfix rather than as an extra transport step. The
advantage to using a very mature piece of software like MIMEDefang
instead of writing your own is that you will be able to benefit from
years of testing by thousands of sites with billions of messages and a
great deal of refinement of the code over those years.
--
Now where did I hide that website...
Hi ,
Is direclty using milter better or using mimedefang would be better.
What are the pros and cons of each other.
Raan
On Nov 6, 12:52 am, Bill Cole
> In article <1193976408.215518.316...@v29g2000prd.googlegroups.com>,
>
> Raan
> > Hi ,
>
> > I want to develop a solution in which all of the mails with attachment
> > will undergo a minor change i.e i will add some kind of watermarking.
>
> > For that i want to develop some kind of smtp proxy server which will
> > do the work of watermarking , further it will forward the mail to
> > actual smtp server.
>
> > Any pointers related to development of proxy server would be really
> > helpful.
>
> I suggest that you don't do this, particularly if you are desperate
> enough for clues on how to proceed that you are asking here. A lot of
> people have written tools to do this sort of thing, and a very large
> fraction of them have been done quite badly. There are significant
> subtleties with an MTA making changes to a message body, and doing it in
> the safest possible way is not always simple.
>
> Instead, I suggest that you look at MIMEDefang
> (http://www.mimedefang.org) which is a free "Milter" program that can do
> exactly what you describe except that it does so as a plug-in to
> Sendmail or Postfix rather than as an extra transport step. The
> advantage to using a very mature piece of software like MIMEDefang
> instead of writing your own is that you will be able to benefit from
> years of testing by thousands of sites with billions of messages and a
> great deal of refinement of the code over those years.
>
> --
> Now where did I hide that website...
On 11/12/2007 5:30 AM, Raan wrote:
> Is direclty using milter better or using mimedefang would be better.
MIMEDefang is a milter.
> What are the pros and cons of each other.
As Bill Cole pointed out, MIMEDefang is very well tested as well as
being extensible. There is also a large user base / support base with
MIMEDefang that you can call on for support if you need it.
Grant. . . .
Raan wrote:
> Is direclty using milter better or using mimedefang would be better.
It depends on what you're trying to do. "Directly" using milter,
I assume, means using Sendmail's reference libmilter and writing your
filter in C.
> What are the pros and cons of each other.
MIMEDefang is written in Perl. Using libmilter directly means writing
C or C++ code. So:
Pros of MIMEDefang:
o Perl is way more appropriate than C for mangling chunks of text.
o MIMEDefang is much easier to start using than straight libmilter.
o You can take advantage of 100001 CPAN modules, so your filter is probably
98% written already.
o You don't need to worry about buffer overflows, pthreads
synchronization issues, etc. because those issues have be taken care
of by MIMEDefang. (I'm fairly confident of that, anyway!)
Cons of MIMEDefang:
o Perl uses way more memory than C (unless you write bizarre C.)
o Perl is potentially much slower than C, depending on what you're trying to do.
o MIMEDefang doesn't map all of libmilter's callbacks, so you do lose a little
flexibility.
All in all, I'd strongly recommend going with MIMEDefang first because
you can whip up a filter in a few minutes. Then if (and only if) you
determine that the function can't be done efficiently/effectively in
Perl, write a C milter.
Regards,
David.
Hi All,
Thanks for providing me information.
I have one more question specific to MIMEDefang.
I want to change my attachment say abc.doc to encrypted abc.doc.
I was searching for various methods available but I could only find
the method for changing the attachment with URL. I could not find any
method that could replace my attachment .
Can you tell me how can I only replace the attachment of the mail with
another document.
Rgds,
Raan
On Nov 13, 11:19 am, "David F. Skoll"
> Raan wrote:
> > Is direclty using milter better or using mimedefang would be better.
>
> It depends on what you're trying to do. "Directly" using milter,
> I assume, means using Sendmail's reference libmilter and writing your
> filter in C.
>
> > What are the pros and cons of each other.
>
> MIMEDefang is written in Perl. Using libmilter directly means writing
> C or C++ code. So:
>
> Pros of MIMEDefang:
>
> o Perl is way more appropriate than C for mangling chunks of text.
> o MIMEDefang is much easier to start using than straight libmilter.
> o You can take advantage of 100001 CPAN modules, so your filter is probably
> 98% written already.
> o You don't need to worry about buffer overflows, pthreads
> synchronization issues, etc. because those issues have be taken care
> of by MIMEDefang. (I'm fairly confident of that, anyway!)
>
> Cons of MIMEDefang:
>
> o Perl uses way more memory than C (unless you write bizarre C.)
> o Perl is potentially much slower than C, depending on what you're trying to do.
> o MIMEDefang doesn't map all of libmilter's callbacks, so you do lose a little
> flexibility.
>
> All in all, I'd strongly recommend going with MIMEDefang first because
> you can whip up a filter in a few minutes. Then if (and only if) you
> determine that the function can't be done efficiently/effectively in
> Perl, write a C milter.
>
> Regards,
>
> David.
On 11/13/07 20:54, Raan wrote:
> Thanks for providing me information.
*nod*
> I have one more question specific to MIMEDefang.
Ok...
> I want to change my attachment say abc.doc to encrypted abc.doc.
Ew, that is not a question. That is an entire 55 galen drum of worms,
if not multiple.
> I was searching for various methods available but I could only find
> the method for changing the attachment with URL. I could not find any
> method that could replace my attachment .
Really, it's going to be the same procedure as used to replace the
attachment with a URL. That is to say you will be identifying and
removing the attachment, processing it, and putting something back in
its place. In your case you are just wanting to put an encrypted
attachment back verses a URL.
> Can you tell me how can I only replace the attachment of the mail
> with another document.
Encrypting the attachment is not as easy as you might think. You have
to have support with in the attachment in question for encryption or you
have to use an encrypting wrapper. There is also the problem of what
encryption method / key do you use based on each recipient.
If you are just wanting to protect the message and its included
attachment(s) from prying eyes I suggest that you look at encrypting the
entire message including attachment(s). Presently S/MIME and PGP are
the two main standards that I'm aware of.
Is it possible to come up with something to take a non encrypted message
and encrypt it, sure. However you will still have to deal with which
encryption key to use based on which recipient.
Grant. . . .
Raan wrote:
> I have one more question specific to MIMEDefang.
> I want to change my attachment say abc.doc to encrypted abc.doc.
[...]
> Can you tell me how can I only replace the attachment of the mail with
> another document.
You need to use the MIME::Tools interface to do that. See the
following man pages for starting points:
mimedefang-filter
MIME::Entity
Regards,
David.
Hi All,
Thanks for your input.
My encryption mechanism and software is already developed as
webservice , and it is already used by other applications.
Thus the key management and encryption mechanism is already available
as web service.
Now i have to plugin to sendmail. We have already thought of all
issues related to key and encryption.
But i m newbie to sendmail and mimedefang.
I want to perform the following things
1. Storing the document in some place.
2. Calling the web service from the filter or filter-end method and
storing the returned encrypted file.
3. Changing the attachment with new attachment.
thus i have two questions
First is related to MIMEdefang. how can i change the attachment in
mimedefang ?
Second is it possible to call web service from perl ?
Regards,
Raan
On Nov 15, 1:07 am, Grant Taylor
> On 11/13/07 20:54, Raan wrote:
>
> > Thanks for providing me information.
>
> *nod*
>
> > I have one more question specific to MIMEDefang.
>
> Ok...
>
> > I want to change my attachment say abc.doc to encrypted abc.doc.
>
> Ew, that is not a question. That is an entire 55 galen drum of worms,
> if not multiple.
>
> > I was searching for various methods available but I could only find
> > the method for changing the attachment with URL. I could not find any
> > method that could replace my attachment .
>
> Really, it's going to be the same procedure as used to replace the
> attachment with a URL. That is to say you will be identifying and
> removing the attachment, processing it, and putting something back in
> its place. In your case you are just wanting to put an encrypted
> attachment back verses a URL.
>
> > Can you tell me how can I only replace the attachment of the mail
> > with another document.
>
> Encrypting the attachment is not as easy as you might think. You have
> to have support with in the attachment in question for encryption or you
> have to use an encrypting wrapper. There is also the problem of what
> encryption method / key do you use based on each recipient.
>
> If you are just wanting to protect the message and its included
> attachment(s) from prying eyes I suggest that you look at encrypting the
> entire message including attachment(s). Presently S/MIME and PGP are
> the two main standards that I'm aware of.
>
> Is it possible to come up with something to take a non encrypted message
> and encrypt it, sure. However you will still have to deal with which
> encryption key to use based on which recipient.
>
> Grant. . . .
On 11/14/07 22:11, Raan wrote:
> Thanks for your input.
You are welcome.
> My encryption mechanism and software is already developed as
> webservice , and it is already used by other applications. Thus the
> key management and encryption mechanism is already available as web
> service.
Ok...
> Now i have to plugin to sendmail. We have already thought of all
> issues related to key and encryption.
....
> But i m newbie to sendmail and mimedefang.
>
> I want to perform the following things
>
> 1. Storing the document in some place.
> 2. Calling the web service from the filter or filter-end method and
> storing the returned encrypted file.
> 3. Changing the attachment with new attachment.
Hum... (See below.)
> thus i have two questions
>
> First is related to MIMEdefang. how can i change the attachment in
> mimedefang ?
I don't have any experience so I can't say for sure. Seeing as how
MIMEDefang is written in Perl and Perl has the tools / libraries to read
MIME structures and alter them I see no reason why you could not use
MIMEDefang to run your own Perl code to do that. David?
> Second is it possible to call web service from perl ?
Again I have not done it my self, but I have done many other things from
Perl including writing my own SMTP engine and used other libraries to
pull (HTTP GET) data from web servers. I see no reason why you could
not write something that communicates with web pages. If you do go this
route, I'd recommend that you look in to how things like SOAP work (with
XML) so you are not screen scraping.
However based on the method that you have out lined above, I would
suggest that you not do this as a milter but rather as a delivery agent.
That is to say I'd recommend that you use something like MailerTable
to route messages that need to be encrypted in to your encryption
gateway mailer (delivery agent). Have said mailer deliver the message
in to a queue and finish the SMTP process. Then you could have another
process take the message and use the web app that you have in place and
take the output and re-mail it to the proper recipient as an entirely
new message. Now if your web app was a front end to an encrypting back
end, you might be able to have a milter communicate with the same back
end code.
I think I would seriously evaluate whether or not this qualifies (as I
understand what you have laid) as a process that should run in a milter
or not.
Grant. . . .