In this there are 3 methods to resolve this issue.

1. First is “Disable work Offline”.
2. Next method is “Reconfirm E-mail account setting”. Go to file and select account setting.
3. Select the E-mail account and click on change button.
4. Re-enter the all required information.
5. Click on more setting button.
6. Click on advanced tab and enter the incoming and outgoing port numbers.
7. Click on “Finish” button.
8. Next method is “Disable Add-ins”. Click on “File” and select “Options”.
9. Click on “Add-ins”.Select Go option from the bottom.
10. Un-check all “Add-Ins”.

Know how to Troubleshoot Outlook 2013 not able to send and receive emails.