Some of the possible reason for this delay could be related connection issue, spam filtering or offline server. I think you are using Outlook 2010. Also try to turn off your anti-virus software and now try again. Also you can perform some troubleshooting steps like :
- In Exchange server 2010, open toolbox -> mail flow troubleshooter and enter a label for analysis and select 'messages destined to recipients are delayed'.
- Click next and enter the server name and GC name. Now enter sender and recipient's email address. Click nest twice.
Export the reports and save it as .xml file. Then compress the file and after it upload it to
www.skydrive.live.com for testing.
Regards
Sarah