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Old 10-21-2009, 01:26 AM   #1
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Default Can ISP block selected e-mails?

Hi. I think i'm this is the right place to ask this question.

I'm not interested in legal aspect, just technical. I know it's not right. But there are still governments which practice censorship.

I'm not asking about spam filters. Those can be applied by mail service providers, which is different from ISP. Say my mail SP is Yahoo Mail, my ISP is Comcast for example. Comcast is not controlling Yahoo severs. But can control traffic from Yahoo server to me. Right?

The situation: ISP blocked a website. Now most likely it will try to filter subscribed distribution mail from this site.

Can an ISP filter my emails using information in the headers? The e-mail which I access through browser (not an e-mail client)

If yes, Can this be avoided?

Apparently I'll see the subject line, but will I'll be able to receive the body of the mail? The text? What if there is no text just attachment, say zip file?
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Old 10-21-2009, 09:39 AM   #2
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Default Re: Can ISP block selected e-mails?

ummm...
the question is very specific, but also very vague...

look at it this way...
when an ISP blocks a website, usually they are blocking the connection to a specific IP address,

so an ISP can feasibly drop all traffic from a specific range. this could be Yahoo servers, this would be a complete deny... so you wouldn't get any emails and never know that an email had been sent...

now, can an ISP take a message desitned for your IP address, feasibly and ISP could block port 25 to stop you getting sent emails, but this would be a complete block, not a block from a certain person.

if your ISP relays your message (at the actual message level using SMTP) then they could filter the message in the same way a spam filter would/could so they could do whatever they liked from it.

can an ISP stop you looking at your Yahoo messages on their webmail?
filter out the message part leaving only the message headers?

no.
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Old 10-21-2009, 10:48 AM   #3
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Default Re: Can ISP block selected e-mails?

Quote:
Originally Posted by root View Post
ummm...
the question is very specific, but also very vague...

look at it this way...
when an ISP blocks a website, usually they are blocking the connection to a specific IP address,

so an ISP can feasibly drop all traffic from a specific range. this could be Yahoo servers, this would be a complete deny... so you wouldn't get any emails and never know that an email had been sent...

now, can an ISP take a message desitned for your IP address, feasibly and ISP could block port 25 to stop you getting sent emails, but this would be a complete block, not a block from a certain person.

if your ISP relays your message (at the actual message level using SMTP) then they could filter the message in the same way a spam filter would/could so they could do whatever they liked from it.

can an ISP stop you looking at your Yahoo messages on their webmail?
filter out the message part leaving only the message headers?

no.
The reason I'm asking I had experience. In Uzbekistan I tried to open some of my messages but I was getting message from the ISP about an error. Those were plain text, but contained censored words like "Andijan" "massacre" "government". I could access the site, could log in and see the list of e-mails, but couldn't open some. While others were perfectly accessible. That was web-based service - yahoo mail.
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Old 10-21-2009, 11:04 AM   #4
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Default Re: Can ISP block selected e-mails?

hmmm...

I suppose that it's be possible to filter the service with a web based proxy server that scanned the page in real time for banned keywords...

so as you load a page it scans what you're looking at...

what I'd suggest.. if you can use HTTPS for yahoo mail then do.
also try using the newer java based yahoo mail webclient that's (I guess) supposed to look more like outlook than the old yahoo mail. it might be harder for them to scan/block information presented from the Java client than the plain text web version.
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Old 10-21-2009, 11:23 AM   #5
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Default Re: Can ISP block selected e-mails?

What if there was no text in the body of the message? just an attached file, say zip or PDF, would it be possible to access it? Can provider block it?
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Old 10-22-2009, 06:16 AM   #6
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Default Re: Can ISP block selected e-mails?

I'd say usually no.
emailed files are encoded in base 64 mime types, they'd have to re-assemble the file and open the file and scan for banned words.

theoretically possible, but requires too much hard work I'd imagine.
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I didn’t fight my way to the top of the food chain to be a vegetarian…
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"The inherent vice of capitalism is the unequal sharing of blessings; The inherent vice of socialism is the equal sharing of miseries."
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