Re: Suggestions / Gotchas - Linux as mail proxy to MS Exchange
From: Harry Phillips (harry_at_hkjsfh.com)
Date: 08/23/03
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Date: Sun, 24 Aug 2003 00:35:05 +1000
Adam wrote:
> The company I work for is looking into setting up a Linux proxy that
> will sit between the internet (incoming mail to the domain) and our MS
> exchange server. We need the Linux box to do the following:
I have done this setup for a client of mine, though for different
reasons. The stupid Exchange plug-in that is supposed to grab e-mail
from a POP3 mailbox and deliver it locally wouldn't stay running.
>
> 1.) Filter spam with a reasonably good spam filter. By filter I mean
> something to the effect of mail that is almost certainly spam can be
> deleted and mail that has a 50/50 chance of being spam may be marked
> as possible spam but passed on to the exchange server.
Well I suggest (as others have already) spamassassin.
It will give it a score if it likely to be spam. Anything above 15 goes
straight to /dev/null, anything above 5 is considered Spam and placed in
a Spam IMAP folder. You could set it up to send the message to a
particular e-mail account.
>
> 2.) Filter e-mails with attachments. We would like to be able to
> specify that e-mails that have an attachment with an .XXX extension be
> deleted. (My department head is thinking we just want to delete the
> entire message, but realistically removing the attachment may suffice
> once he thinks it through.)
mmm... don't know about specific extensions but if I look in a message
with an attachment I see the text:
Content-Disposition: attachment; filename=
You can always get procmail to look for that text and send it to a
particular Exchange Account.
>
> 3.) Scan e-mails for viruses and clean as necessary.
Don't know about this one. I don't need it, I run a Mandrake desktop.
>
> After mail passes through all 3 of the above stages, it would be
> forwarded over to the exchange server and all would be good. :)
This is easy. In your /etc/hosts file you add the entry:
----
192.168.1.254 exchange.company exchange
----
Substitute the right IP for your Exchange of course. Then all you need
to do is have the right entries in the /etc/procmailrc to forward the
mail to the Exchange server. As an example:
----
:0c
* ^TO_abyram@ia.ua.edu
! abyram@exchange
:0c
* ^TO_next-user@ia.ua.edu
! next-user@exchange
:0c
* ^TO_last-user@ia.ua.edu
! last-user@exchange
:0
/dev/null
----
In case you don't know. The rules that start with :0c is so that the
mail doesn't hit the first match and stop. It keeps going to the next rule.
This is important because a single message might be sent to you and
'next-user', if you don't have the :0c only you will receive the message.
So the order of the rules I would use:
1. Send it to SpamAssassin to check it.
2. If it is above 15 send it to /dev/null
3. Look for attachments and send the message to a separate Exchange
account (eg. attachments@exchange)
4. Send a copy of the message to anyone it is addressed to.
5. Send the message to /dev/null
Only do the last one if you don't want to keep a copy of the message.
BTW The client I implemented this setup for kept a copy of all incoming
messages separate on the Linux box. When presented with evidence of
e-mails received a disgruntled employee dropped their court case.
>
> Now, what I am hoping someone here can tell me is:
>
> 1.) What programs are suggested for the tasks we need as outlined
> above?
fetchmail
spammassassin
procmail
>
> 2.) If anyone has already done this or has looked into it very deeply,
> do you have any suggestions of what the best way to go about this is
> and are there any gotchas we should be on the look out for?
Um, the above setup was for a single catch-all POP3 mail account hosted
by their domain hosts. We used fetchmail to check it every three minutes.
--
Regards,
Harry Phillips
--- Failure is not an option,
it comes bundled with your Microsoft product.
- Next message: Timmy: "Re: I have a question."
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- In reply to: Adam: "Suggestions / Gotchas - Linux as mail proxy to MS Exchange"
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