Email, Linux and procmail for children

My son is 6 years old. I think that it is just about time for him to
learn email, however, I want to make sure that he is 100% safe.

Since we use linux, I am free to mess with sendmail, procmail, etc.

So my plan for now is to limit who he can receive emails from. Let's
say he can receive email from dad, mom, and a couple of his
friends. Just a list of valid From: emails.

All other email from other people would be forwarded to me.

Another thing that I want is to get carbon copies of his outgoing
email. Can I somehow make sendmail do that?

Does this make any sense.

i

Re: Email, Linux and procmail for children

In comp.os.linux.misc Ignoramus2043 wrote:
> My son is 6 years old. I think that it is just about time for him to
> learn email, however, I want to make sure that he is 100% safe.
>
> Since we use linux, I am free to mess with sendmail, procmail, etc.
>
> So my plan for now is to limit who he can receive emails from. Let's
> say he can receive email from dad, mom, and a couple of his
> friends. Just a list of valid From: emails.

You are aware hopefully that anyone can send email from "dad, mom,
and a couple of his friends"? Spammers found out long ago
how to get around "white lists"

100% safe is not possible with email unless you are talking
about your own private closed network.

>
> All other email from other people would be forwarded to me.
>
> Another thing that I want is to get carbon copies of his outgoing
> email. Can I somehow make sendmail do that?

forwarding/ cc's and the like are quite doable.
>
> Does this make any sense.
>

Sure- except that you may have unrealistic expectations.

IF you set up and rigorously maintain spam filters, firewalls,
white lists and so on, then you can be fairly certain that
you can block unwanted email. But spammers are very good
at what they do and you _will_ get some unwanted material
through sooner or later.

Or you could limit all email traffic to your own private network
and not accept any email from outside of it. That's quite doable
with firewall but it would be problematic with "a couple of his friends"
unless you give them access to your network.


Stan
--
Stan Bischof ("stan" at the below domain)
www.worldbadminton.com

Re: Email, Linux and procmail for children

On 2007-11-15, stan@worldbadminton.com wrote:
> In comp.os.linux.misc Ignoramus2043 wrote:
>> My son is 6 years old. I think that it is just about time for him to
>> learn email, however, I want to make sure that he is 100% safe.
>>
>> Since we use linux, I am free to mess with sendmail, procmail, etc.
>>
>> So my plan for now is to limit who he can receive emails from. Let's
>> say he can receive email from dad, mom, and a couple of his
>> friends. Just a list of valid From: emails.
>
> You are aware hopefully that anyone can send email from "dad, mom,
> and a couple of his friends"? Spammers found out long ago
> how to get around "white lists"

So, how would an automated spammer figure out that they should spam my
son's account with my email?

>>
>> Does this make any sense.
>>
>
> Sure- except that you may have unrealistic expectations.
>
> IF you set up and rigorously maintain spam filters, firewalls,
> white lists and so on, then you can be fairly certain that
> you can block unwanted email. But spammers are very good
> at what they do and you _will_ get some unwanted material
> through sooner or later.

It is not spammers that I am worried about, I am more worried about
private assholes.

> Or you could limit all email traffic to your own private network
> and not accept any email from outside of it. That's quite doable
> with firewall but it would be problematic with "a couple of his friends"
> unless you give them access to your network.

i

Re: Email, Linux and procmail for children

In comp.os.linux.misc Ignoramus2043 wrote:
> On 2007-11-15, stan@worldbadminton.com wrote:
>> In comp.os.linux.misc Ignoramus2043 wrote:
>
> So, how would an automated spammer figure out that they should spam my
> son's account with my email?
>

Umm-- your son sends an email across the open net, you send one also,
spammer engine puts two and two together and sends one to him using
your return address? Since both are at the same domain it is a
reasonable bet that this will get around whitelists.

this isn't rocket science. Why do you think spam
is such a problem?

SMTP is open plain text and not what anyone would call secure.

Stan
--
Stan Bischof ("stan" at the below domain)
www.worldbadminton.com

Re: Email, Linux and procmail for children

On 2007-11-15, stan@worldbadminton.com wrote:
> In comp.os.linux.misc Ignoramus2043 wrote:
>> On 2007-11-15, stan@worldbadminton.com wrote:
>>> In comp.os.linux.misc Ignoramus2043 wrote:
>>
>> So, how would an automated spammer figure out that they should spam my
>> son's account with my email?
>>
>
> Umm-- your son sends an email across the open net, you send one also,
> spammer engine puts two and two together and sends one to him using
> your return address? Since both are at the same domain it is a
> reasonable bet that this will get around whitelists.

I get about 1,000 spams per day (filtered by spamassassin) and I never
had this happen.

> this isn't rocket science. Why do you think spam is such a problem?

Because most people cannot use whitelists. (as in "whitelisted
only").

> SMTP is open plain text and not what anyone would call secure.

Yes, but as a matter of fact, spammers do not use the technique that
you mentioned. Partly because it is easy to detect with spamassassin
(local email comes from untrusted networks).

i

Re: Email, Linux and procmail for children

On 11/15/07 11:59, Ignoramus2043 wrote:
> My son is 6 years old. I think that it is just about time for him to
> learn email, however, I want to make sure that he is 100% safe.

Good for you and good luck to you. 100% safe is not really possible,
but 95+% is probably acceptable.

> Since we use linux, I am free to mess with sendmail, procmail, etc.

Indeed.

> So my plan for now is to limit who he can receive emails from. Let's
> say he can receive email from dad, mom, and a couple of his friends.
> Just a list of valid From: emails.
>
> All other email from other people would be forwarded to me.

I would actually suggest that you do it a bit different. Have what
people believe is your son's email address be an additional email
address that you check. Have a separate email address that is really
what your son checks. Then you will be the front line that receives all
email to your son's email address. The messages that you want your son
to have you would need to forward on to his internal account. Or if you
are running IMAP, you could copy messages from his public address to his
private address. This way only what you want to get to your son gets to
him. Granted this presumes that something is in place to make sure that
no one can email your son directly, be it protected recipients / senders
with Sendmail or something else.

If you want to set up a procmail recipe to automatically forward a copy
of messages from known good senders on to son, you can do so relatively
easily.

Something else you might consider is requiring people that you want to
have the ability to send to your son automatically to include a string
with in the message as a simple quick verification that the message is
more than just a spam cannon, say something like a family nick name. I
know that this is not fool proof, but it is a simple second check that
needs to be checked off that most spam will not do even if it could do it.

> Another thing that I want is to get carbon copies of his outgoing
> email. Can I somehow make sendmail do that?

As far as getting a CC of what your son sends out, you can do that many
different ways. You can do any thing with his MUA adding a CC all the
way up to a milter and / or Sendmail config that adds an additional
recipient to his messages. It depends on what you want to do and where
you want to do it.

> Does this make any sense.

Yes. I also commend you for both 1) trying to safely expose your son to
technology and 2) trying to do it as safely as possible.



Grant. . . .

Re: Email, Linux and procmail for children

wrote in message
news:473c9b07$0$14082$742ec2ed@news.sonic.net...
> In comp.os.linux.misc Ignoramus2043 wrote:
> > On 2007-11-15, stan@worldbadminton.com wrote:
> >> In comp.os.linux.misc Ignoramus2043
wrote:
> > So, how would an automated spammer figure out that they should spam my
> > son's account with my email?
>
> Umm-- your son sends an email across the open net, you send one also,
> spammer engine puts two and two together and sends one to him using
> your return address? Since both are at the same domain it is a
> reasonable bet that this will get around whitelists.

How do you conclude that? Same domain could mean that the message should never
leave the domain (or host), yet when it comes in from an IP address (or domain)
external to their domain, what makes you think that they couldn't automatcally
tell it's a forgery? Granted, this will require that they add some custom rules
since such detecton isn't necessarily the default (SPF per RFC 4408 ignored for
the moment - considered as a "custom rule" for this discussion)....

> this isn't rocket science. Why do you think spam
> is such a problem?

Because PEOPLE are the problem.

> SMTP is open plain text and not what anyone would call secure.

That's about the only correct thing you said.

> Stan

Re: Email, Linux and procmail for children

["Followup-To:" header set to comp.os.linux.misc.]
Ignoramus2043 :
>
> So, how would an automated spammer figure out that they should spam my
> son's account with my email?

No need. Windows supports viruses which will scrape users' mailboxes
and address books for potential victims. You send mail to a Windows
user, and you'll get crap from third parties in return.


--
Any technology distinguishable from magic is insufficiently advanced.
(*) http://blinkynet.net/comp/uip5.html Linux Counter #80292
- - http://www.faqs.org/rfcs/rfc1855.html Please, don't Cc: me.

Re: Email, Linux and procmail for children

Ignoramus2043 wrote:

> My son is 6 years old. I think that it is just about time for him to
> learn email, however, I want to make sure that he is 100% safe.

Personal opinion: I think a 6-year-old is too young to have access to
e-mail.

Ok, that aside: I have e-mail accounts set up for my 13-year-old. Since we
produce a commercial anti-spam solution, I use features of that solution
that only allow whitelisted senders to send to my child; all other mail
gets held for me to review. (And my child does not have login access
to the anti-spam solution.)

If you don't want a commercial solution, you can do something pretty
similar with MIMEDefang (http://www.mimedefang.org) which is in fact
the basis of our commercial solution.

> So my plan for now is to limit who he can receive emails from. Let's
> say he can receive email from dad, mom, and a couple of his
> friends. Just a list of valid From: emails.

> All other email from other people would be forwarded to me.

> Another thing that I want is to get carbon copies of his outgoing
> email. Can I somehow make sendmail do that?

Both of those tasks are very easy with MIMEDefang and a smattering of
Perl code.

Note that all of my careful safeguards have not prevented my child
from signing up for a Gmail account, so... at some point you have to
use common sense like not giving your kids computers in their own
rooms and not letting young kids use the Internet unsupervised.

Regards,

David.

Re: Email, Linux and procmail for children

Ignoramus2043 wrote:

> On 2007-11-15, stan@worldbadminton.com wrote:
>> In comp.os.linux.misc Ignoramus2043 wrote:
>>> My son is 6 years old. I think that it is just about time for him to
>>> learn email, however, I want to make sure that he is 100% safe.
>>>
>>> Since we use linux, I am free to mess with sendmail, procmail, etc.
>>>
>>> So my plan for now is to limit who he can receive emails from. Let's
>>> say he can receive email from dad, mom, and a couple of his
>>> friends. Just a list of valid From: emails.
>>
>> You are aware hopefully that anyone can send email from "dad, mom,
>> and a couple of his friends"? Spammers found out long ago
>> how to get around "white lists"
>
> So, how would an automated spammer figure out that they should spam my
> son's account with my email?

They don't care. But by chance they may use one of the whitelisted
addresses for spamming.



>> Sure- except that you may have unrealistic expectations.
>>
>> IF you set up and rigorously maintain spam filters, firewalls,
>> white lists and so on, then you can be fairly certain that
>> you can block unwanted email. But spammers are very good
>> at what they do and you _will_ get some unwanted material
>> through sooner or later.
>
> It is not spammers that I am worried about, I am more worried about
> private assholes.

That's more difficult as it should not be that difficult for a "private
asshole" to figure out some of the whitelisted addresses.

Signing mails (using GnuPG or similar) could be a solution for mom and
dad, but I doubt it will work for his frieds.



Florian
--

------------------------------------------------------------ -----------
** Hi! I'm a signature virus! Copy me into your signature, please! **
------------------------------------------------------------ -----------

Re: Email, Linux and procmail for children

Ignoramus2043 wrote:
> My son is 6 years old. I think that it is just about time for him to
> learn email, however, I want to make sure that he is 100% safe.

> So my plan for now is to limit who he can receive emails from [...]
> All other email from other people would be forwarded to me.

The way I have this set up is that my children's email gets delivered
to me (and put into specific folders, one for each). If I "approve" the
email I then move it into the appropriate inbox for the child and they
"have new mail". (Dovecot's IMAP implementation lets me do this quite
straightforwardly.)


> Another thing that I want is to get carbon copies of his outgoing
> email. Can I somehow make sendmail do that?

I can see my children's Sent mailbox. Would that be sufficient for you?
(Same configuration approach within Dovecot as for INBOX.)

If you don't use Dovecot you might find symlinks from within your
mailbox tree to your child's inbox and sent box would be sufficient.
I've not tested this, though.

Chris

Re: Email, Linux and procmail for children

On 11/16/07 06:17, Chris Davies wrote:
> The way I have this set up is that my children's email gets delivered
> to me (and put into specific folders, one for each). If I "approve"
> the email I then move it into the appropriate inbox for the child and
> they "have new mail". (Dovecot's IMAP implementation lets me do this
> quite straightforwardly.)

I had considered implementing IMAP too. However not as many people are
aware of how nice an IMAP environment can be and as such don't have
support for it. Thus I went a different route. All in all I think IMAP
may be better.

> I can see my children's Sent mailbox. Would that be sufficient for
> you? (Same configuration approach within Dovecot as for INBOX.)

I wonder if we could come up with something that would allow any
messages from specific addresses to have their envelope recipient
altered to be the parent's mail box. Then the parent could 'approve'
(as you say) all messages before they leave the network. I guess in
effect the parent becomes much like a proxy / bastion host for the
child's email.

> If you don't use Dovecot you might find symlinks from within your
> mailbox tree to your child's inbox and sent box would be sufficient.
> I've not tested this, though.

Or at the very least, put both IMAP accounts with in the same MUA and
drag and drop messages between them.



Grant. . . .

Re: Email, Linux and procmail for children

On 11/15/07 11:59, Ignoramus2043 wrote:
> So my plan for now is to limit who he can receive emails from. Let's
> say he can receive email from dad, mom, and a couple of his friends.
> Just a list of valid From: emails.

Another idea that is probably more Sendmail centric than any thing else
that I have seen so far is to have all messages going to your son be
quarantined via Sendmail's quarantining mechanism. Thus all messages in
would be held for approval. You could go in to the queue and find all
quarantined messages and either approve or reject them at your
discretion. I'm sure there are also ways to re-direct the messages
where ever you would like.

> Another thing that I want is to get carbon copies of his outgoing
> email. Can I somehow make sendmail do that?

Quarantining messages from your son (with a different quarantine reason
for filtering / reporting / querying purposes) would also allow you to
to handle messages going out from your son as well.

Quarantining would allow you to in effect have the ability to "approve"
messages like Chris Davis was saying.



Grant. . . .

Re: Email, Linux and procmail for children

Florian Diesch (diesch@spamfence.net) writes:

> Signing mails (using GnuPG or similar) could be a solution for mom and
> dad, but I doubt it will work for his frieds.
>
But since the only people who would be sending email to the child are
those who are known, and likely well known, surely one can ask
them to either add a header with some "magic word" or just put
the "magic word" in the subject header. Then filter on that, though
I suppose one might have to check to make sure nothing gets lost
when someone forgets the "magic word".

This is not that different from being six years old and waiting for
mail to come through the mail slot. This is just a modern version,
and of course the modern version requires a few more safeguards.

ANd at that age, the people sending mail would be relatives or
friends of my parents. Even a bit later, it was unusual to get
mail from a peer, though when that happened I'm sure they had help.
So it's not likely unrealistic to expect any email to come to this
email address to be coming from an adult, or a child with adult's
help. Hence, the "magic word" is something doable.

Michael

Re: Email, Linux and procmail for children

On 11/16/07 10:19, Michael Black wrote:
> But since the only people who would be sending email to the child are
> those who are known, and likely well known, surely one can ask them
> to either add a header with some "magic word" or just put the "magic
> word" in the subject header. Then filter on that, though I suppose
> one might have to check to make sure nothing gets lost when someone
> forgets the "magic word".

Adding the "magic header" is a nice idea. However I think doing so will
be extremely problematic in most modern non-unix MUAs. I personally
don't know how to add a header in any version of Outlook, do you?

> This is not that different from being six years old and waiting for
> mail to come through the mail slot. This is just a modern version,
> and of course the modern version requires a few more safeguards.

All be it the idea is similar, this is not really that good a comparison
because email does not cost postage and materials like snail mail does.
It is exponentially easier and cheaper to send junk email than it is
junk snail mail.

> And at that age, the people sending mail would be relatives or
> friends of my parents. Even a bit later, it was unusual to get mail
> from a peer, though when that happened I'm sure they had help. So
> it's not likely unrealistic to expect any email to come to this email
> address to be coming from an adult, or a child with adult's help.
> Hence, the "magic word" is something doable.

What if a child's name gets put on to a mailing list? It is just less
likely that they will bet junk mail at that age, not impossible.



Grant. . . .

Re: Email, Linux and procmail for children

Ignoramus2043 writes:

> My son is 6 years old. I think that it is just about time for him to
> learn email, however, I want to make sure that he is 100% safe.
>
> Since we use linux, I am free to mess with sendmail, procmail, etc.
>
> So my plan for now is to limit who he can receive emails from. Let's
> say he can receive email from dad, mom, and a couple of his
> friends. Just a list of valid From: emails.
>
> All other email from other people would be forwarded to me.
>
> Another thing that I want is to get carbon copies of his outgoing
> email. Can I somehow make sendmail do that?
>
> Does this make any sense.

As it has been said int other posts in the thread:
verification based on From: (or "MAIL FROM:") is not "fake resistant".

You can (sufficiently) reliably verify sender if:
a) message has been submitted locally via SMTP AUTH
*OR*
b) messages has been passed from a mail server generating *trustworthy*
headers that can be used for sender verification

Option "b" is "service dependent" so you would have to name specific
email service you would like to "parse" and post sample headers
generated by such service.


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Open-Sendmail: http://open-sendmail.sourceforge.net/