E-mail messages are not automatically sent or received at startup in Outlook

Method 1: The easiest is to look at your Disable Scheduled Send/Receive option, located under Tools->Send/Receive settings. If this is checked, there's a chance unchecking it could solve the problem.
If above step doesn't work
Method 2:To resolve this behavior, create a new Send/Receive group in Outlook:

1. On the Tools menu, point to Send/Receive Settings, and then click Define Send/Receive Groups
2. Under Group Name, click the group, and then click Copy.
3. Under Send/Receive Group Name, type the new group name, and then click OK.
4. Under Group Name, click the old group name.
5. Under both When Outlook is Online and When Outlook is Offline, click to clear the check box for Include this group in Send/Receive (F9).
6. Click Close.
7. Quit Outlook, and then restart Outlook.

Outlook 2010

To resolve this behavior, create a new Send/Receive group in Outlook:

1. Click File, and then click Options.
2. Click the Advanced tab.
3. In the Find Send and Recieve section, click Send/Recieve.
4. Under Group Name, click the group, and then click Copy.
5. Under Send/Receive Group Name, type the new group name, and then click OK.
6. Under Group Name, click the old group name.
7. Under both When Outlook is Online and When Outlook is Offline, click to clear the check box for Include this group in Send/Receive (F9).
8. Click Close.
9. Quit Outlook, and then restart Outlook.