Take a look here, it may help:
http://www.howto-outlook.com/Faq/mes...ckinoutbox.htm
"abelho" <(E-Mail Removed)> wrote in message
news:3EA03AD9-2669-49BA-B1A7-(E-Mail Removed)...
>I have tried to send an email with an attachment without realising the
> attachment is 26mb. So now it is stuck in my outbox. It has been there all
> day and isn't going anywhere. It is also blocking any other mails I wish
> to
> send.
>
> I have tried to delete the mail but I can't as it says Outlook is
> transmitting the mail.
>
> Does anyone have any ideas about what I can do to get rid of the email
> from
> my outbox?