How to restrict users on email attachments from external mail servers

[Zent User]

I'm using zentyal server as gateway,I want to restrict users on attachments of the external mail servers,how can I implement this ?

[christian]

what do you mean ?
restrict capability to send mail with attachment or to receive mail with attachment ? or something else I didn't catch ?

[Zent User]

I want to restrict on send mail attachments.Suppose one the user using gmail or other external email service to send the mail then I want restrict on attachments on this.He can attach the files upto some limit,lets say 1Mb after that we should not allow him,how can I implement this in Zentyal?

[christian]

hum.... gmail is not mail  from Zentyal standpoint  but HTTP.
So your question is rather how to prevent users to attach files while using external web based applications isn't it?

You could control MIME types but I don't think there is anything available, at least with 2.2 and especially for upload, that would control this using HTTP proxy.

BTW, what's the version you are using?

[christian]

Replying to myself, and for you too, as I made some search:
Squid, technically speaking, could permit to control upload.
e.g. I found something here. Read also next messages in thread 

Traffic shaping will not do 100% what you are looking for but this may give you some ideas too.

[Zent User]

I want to control my team members while attaching the large files in mails.Because it may lead to organization in some way.So I want to protect this.I'm using zentyal 2.2,anyhow thanks for your reply.

[christian]

I made, perhaps wrongly, the assumption that because of @gmail address, your users were using web browser.
This is something you have to understand because if they use browser, then you have to deploy control at HTTP upload level (as I describe in previous answers) while if they use POP client, control has to be done at postfix level where, directly form Zentyal interface, you can limit maximum message size.

[Zent User]

Using Bandwidth Throttling can we control ?

[christian]

Where? in proxy?
In any case, as already explained, you'll face 2 problems:
- upload control => I'm not sure current implementation permits this but rather only download. This could be done however according link I provided. to be investigated.
- bandwidth throttling doesn't aim at "blocking" but shaping traffic so that (usually download) doesn't take all the bandwidth.

[Zent User]

Christian,I've went through the link which you have provided,but where I do specify those settings ? can able to explain briefly

[Zent User]

From previous posts I came to know that there is nothing facility provided to limit on email attachments,So I went through squid document and this link http://www.squid-cache.org/mail-archive/squid-users/200508/0503.html (which is suggested by Christian) then I've modified the squid.conf file and I've added request_body_max_size 1 MB line in squid.conf file,this working only for yahoo mail,its not working for gmail. What might be the reason,this issue is already raised http://www.squid-cache.org/mail-archive/squid-users/201104/0094.html.Please suggest appropriate modification to me,So that I can restrict to uploads without bothering of whether it is a HTTP or HTTTPs.

[Escorpiom]

Gmail is something else, IMAP with another port. No idea how to limit that, I only have it set up in Windows Live mail.

Cheers.

[christian]

This is often confusing for some users: they are sending/reading mail using web (HTTP) interface and think about mail attachment size control or other mail related features while this is not mail but HTTP