Microsoft Outlook for Mac 2011,keeps updating server

i keep getting a message at the bottom of of my Outlook page which says "Updating server." Outlook keeps downloading my e-mails (roughly 18,000). While this process is going on, i can send e-mails but can't receive any. I already rebuilt the Outlook for Mac 2011 database. Do you have any suggestions?

i have a Macbook Pro 15.4" laptop running Yosemite 10.10.3.