Outlook - HTTP - Cannot send normal-sized email

HTML based e-mail is something which should be avoided regardless, since not all e-mail clients support it.

Use plain text in your Composing preferences. If you want someone to see the e-mail in formatted text, get a webhosting account somewhere, and post a link to it. Often internet service providers have limited space for users that can be used for HTML based documents. Seamonkey is a popular free webpage editor. Textwrangler is another, though requires a knowledge of HTML.

If you are sending image attachments beyond your sendmail server's limit, reduce their size with Preview using the Save As command. For better control, use http://www.lemkesoft.com/ 's GraphicConverter. You can often reduce a JPEG to 1/10th is original size and still get decent image quality.

Attachment formatting itself is a crapshoot. Some e-mail programs don't like attachment formatting used by some mail clients while others have no trouble with it. You are better off storing said documents on webspace on your internet provider or webhost, and using a free FTP client to connect to said provider, and provide an http:// link to the document on the webhosting site.

If you have a static IP address, or Dyndns address you can also setup your computer as a webhost that can be downloaded from.

For Outlook problems you may also want to search/ask in the forum devoted to that non-Apple app:

http://www.officeformac.com/ProductForums/Outlook/