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In Outlook 2007 on a domain, I wrote up a sentance of text and attached a 77KB image.

I then sent that email out to 1 person within the domain, but when I checked my Sent box it said the email was 2MB.

That's a massive increase, why does Outlook increase the file size of the email?

Other emails seem to be accurate (like Rich Text emails are ~2KB) and these are stored on the Exchange server until I move it into Archive.

The reason I ask is because it eats up my quota more than it should.

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It is possible that it didn't actually increase it that much, but that the code that displays the size estimates are wildly incorrect. It's also possible that the .PST storage format adds a huge overhead. – Warren P Sep 28 '12 at 22:18
@WarrenP Updated my post a bit. My concern is it eating up my quota. – JBurace Sep 28 '12 at 22:19
How did you attach the image? Did you actually drag and drop the image into Outlook and see the "Attachments: image.jpg (77kb)" or did you open the image in Photo editor and do Ctrl-c and Ctrl-v in Outlook and end up with the image inline in the email? – Mokubai Sep 29 '12 at 0:21
up vote 4 down vote accepted

This is possibly a feature of inserting an image inline into an email via by using Ctrl-C within Paint (or a similar art package) then going to Outlook and using Ctrl-V to get an inline image instead of actually just attaching the image via Explorer.

To show you what is happening I have created two emails, both using a 430kb image as a source. Attaching the email as an actual attachment give me a 444KB email, while the Ctrl-C, Ctrl-V method gets me a 2MB email, and very different results in terms of how the email actually looks as well.

I end up with two emails:
enter image description here

The "attached" 444KB email looks like this:
enter image description here

While the "inline" 2MB email has a picture in the email itself:
enter image description here

The most likely reason for this is that when you copy and paste an image directly into an email then Outlook must decide itself what to do with the image data and probably only compresses it using PNG compression which for large photo type images gives much worse compression. When you actually attach the image by either navigating to the file from the "Attach file" dialog or drag-and-dropping it from Explorer then you are attaching the image file (400KB) itself rather than the image data (2MB) being copied via the clipboard.

Windows Photo Viewer on Windows 7 seems to pass the filename to Outlook and I see the "attached" file size rather than the inline size.

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It's also worth noting that even attaching a file will increase the size of the file usually by 25-33% due to transmission encoding. I'm not sure if Outlook includes that in its size display or not. – Michael Kjörling Aug 5 '13 at 12:36

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