If this is what the DNS area in Networking looks like:
This will commonly cause slow connection speeds when attempting to load any websites/Outlook from outside of a corporate network environment (from home, etc)
Open the registry and remove entries from the following location:
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows NT\DNSClient\"SearchList"="domain1,domain2,domain3"
Reboot the computer to apply the changes and retest connection speeds