"antonov" wrote in message
...
I use it at home... outlook 2003... where do I find the setting? I have
looked for it but couldn't find it


Are you actually connecting to an Exchange mail server (from home to
work through, say, a VPN)? Or are you connecting to an SMTP server?

If you are home and connecting to your own e-mail provider (and not to
your work's Exchange server for their internal e-mail service), you are
probably using POP3 and SMTP mail hosts. You have provided no
information regarding your setup. Have you called your e-mail provider
to ask if there is a quota regarding maximum size for outbound mails?
Maybe you are using a text-only e-mail service that doesn't allow
attachments (300kb would be a huge plain-text mail).

"Will not send it" says absolutely nothing about what is the actual
error that you get from Outlook when attempting to send an e-mail over
300kb in size.