One issue is that the attachment is converted to a fomat acceptable to SMTP, which is much larger than the original item.

David, thanks and maybe that's it.

But, as I mentioned, I copied myself on the email. When I received it (i.e., it had already been transmitted), the attachment still showed as only 58.0 kb. If it had converted to a different and much larger format, wouldn't the attachment now show as much larger?

Andrew

David, thanks and maybe that's it. But, as I mentioned, I copied myself on the email. When I received it (i.e., it had already been transmitted), the attachment still showed as only 58.0 kb. If it had converted to a different and much larger format, wouldn't the attachment now show as much larger? Andrew

Short answer NO

Your attachment does not even exist in any form you would recognize in an email body. Email bodies are still strictly limited to the ASCII character set. The email can only consist of headers and the body of the email (not necessarily technical terms here) So the mail body must include any text, images, links and attachments. ALL represented within the limits of the specification. This limit can also be considered in terms of compatibility. Some mail readers support few of the modern HTML features. Others lots. This is why we sometimes get messages that are at best "wonky". The sender used features, usually of HTML, that the product you are reading in does not support. Using the lowest common denominator often helps greatly with these things. However few people even realise that not all email products are created equal. They will have a preferred product, but rarely do they know anything technical about it or the hoops their message must go through to be transmitted.

Enter mime encoding. It takes Binary objects of all sorts and encodes them as a mime (text) object in the message The final size of mime objects is generally considered to be roughly 2½ times the original. While no so much an issue today, in the days a 5mb mail size limits these increases saw a lot of mail that was under the 5mb limit rejected because it was 7 or 8mb when encoded. The size of the attachment shown in Thunderbird is not the space it occupies in the email it is the size it was when attached. Like much of the email paradigm attachments are largely smoke and mirrors as the "attachment" is nothing of the sort. Other than a bit of text in the body of the email that says Content-Disposition: attachment; which allows the human interface to make the garbled text following into something meaningful. (An attachment)

But please read the Wikipedia article on MIME instead of me regurgitating large chunks of it. The topic of message size can be a very highly technical topic. Especially if you did something like paste into the message as well.

I have seen instances, on my own machine while testing of Microsoft Word placing several hundred kilobytes of text with a single character copied from a word document. ie if this was pasted from word, as it can be a good source of special characters, "½" the email may grow close of 300kb from that action.

Then there is the additional overhead of encoding most outgoing mail as HTML. Pretty much the new normal for most folk. The Thunderbird developers are highly resistant to this and will convert a HTML messages to plain text if they can on sending unless you change default settings. However most email does not go as plain text, if you set a font of size or insert a table of anything that could not be simply expressed in the traditional windows Notepad. Think lists numbered and bulleted etc then the message will increase to cover the addition of HTML elements to describe the document and it's formatting.

Wikipedia link to MIME. https://en.wikipedia.org/wiki/MIME

Matt,

Thanks for your detailed reply. While most of it is (way) over my head, I get the gist: There's nothing unusual or incorrect about my modest sized email and "attachment" ultimately being 5.3 mb in size.

As always, I appreciate your help.

Andrew