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JoeB
Asked: 2011-09-14 12:21:48 +0800 CST

Block certain images from incoming emails

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My company just added 5 of the social networking images to its email signature. Now we have tons of copies of these identical images stored in the software that takes emails and turns them into tickets of some kind (Jira does this, but this isn't the only one we have with this problem).

Is there a way to block these on the SMTP level, or at the Exchange level, if I know the exact image? Maybe there's a way to block a PNG of size 25x25 automatically somehow?

EDIT1

If I stop these at the ticket system level, I will have to do it many times in different places. Still looking for a way to do this at the Exchange level. I found this link after reading the latest answer:

http://technet.microsoft.com/en-us/library/aa998825.aspx

Hoping it or a related topic will have a solution. Thanks again.

EDIT2

Looks like the only way to do this in Exchange is to block by file size, and since they all have different sizes we need 5 rules. This is still simpler for us than blocking at every application point that is storing these images.

Thanks for the help.

email exchange smtp exchange-2010 images

2 Answers

  1. Best Answer

    First you have to define what "block" means. Second you need to know the difference between SMTP and email.

    Blocking things at SMTP level means that the whole message is rejected and never reaches the destination. Normally you don't even see the content.

    This also points out the difference between SMTP and email. SMTP is the protocol to transport an email from point A to point B (via an undefined number of hosts in between). Email is the content that should be delivered and normally is composed of meta information (header) and plain text content (no image, no HTML, no attachment). The MIME addition adds support for multi-part content with plain-text, HTML, attachments, inline-images and the like.

    Knowing this you see, that you can't "block" content at the SMTP level. Blocking is all or nothing. What you need is content filtering; or better content stripping.

    No Mail Transfer Agent (e.g. Exchange) is designed for content stripping. It is designed for mail delivery and (with additions) for content tagging. So you need additional software (inside Exchange) that does this. But as you need additional software, why not stripping the content at the destination (ticket system)?

    You don't have an advantage of stripping content at the MTA level. And you don't have a disadvantage at the destination. The content was transported and received nonetheless.

    And as voretaq7 says: This is a management problem. Signatures are bad. Image signatures are evil. Multiple image signatures are really evil and trigger my spam score. (Signatures are only needed where local laws enforce them)

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  2. Nothing like this can be done easily or reliably AFAIK.

    I suggest you explain to your boss that sticking a bunch of images in your signature is damn near universally frowned upon, and if they don't see the light try explaining how much additional disk space will be required to store all these images in your ticketing system (or how many man-hours to manually remove them).

    Alternatively you can see if your mail software can be configured not to attach the annoying images to email destined for local users.

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