Knowledgebase

1). An antispam or antivirus scanner is scanning outgoing mail.
 Norton antispam plugin is one such program that will cause this problem, but it's not the only one. Disable email scanning in the software settings and try sending your mail.
2). Not setting your default email account.
Using Office 2007 - Go to Tools, E-mail accounts, view or change existing accounts. Verify an account is set as default.
Using Office 2010 – Go to file then info and click Account settings verify an account is set as default.
3). Email attachment is too large
A message can get stuck if it includes an attachment that is too large for email servers to handle. Try reducing the size of the attachments and send it again.
While the message is in outbox opening or deleting email is not possible, instead go to the Send/Receive tab and click Work Offline and once offline, it's easy to fix the problem:  open the message to remove the attachment or reduce its size and re-send it.
4). Email account settings are not properly set
Confirm all the email account settings configurations are set properly from email account to the email server settings for both incoming and outgoing mail server.