Outlook not connecting over SonicWALL IPSec VPN?


Last week, a client of mine who we had just moved to our hosted environment noticed that Outlook was frequently disconnecting from their Exchange Server, and mail was coming in minutes if not hours after it was sent.

I found lots of, “HTTP method detected; examining stream for host header” in the SonicWALL’s logs from the client’s network which got me thinking about RPC/HTTP. Googling that log entry took me to https://www.fuzeqna.com/sonicwallkb/consumer/kbdetail.asp?kbid=3582. While that article didn’t specifically address an Outlook issue, it did confirm that Outlook Anywhere might be getting garbled by the SonicWALL. To test, I cleared both of these on a test machine:

  • On a fast network, connect using HTTP first, and then by using the TCP/IP
  • On a slow network, connect using HTTP first, and then by using the TCP/IP
  • which forced Outlook to use only TCP/IP. In that configuration, Outlook connected immediately and messages were received within seconds. I didn’t want to visit each computer to affect this change and besides, “it used to work.”

    I followed the SonicWALL article’s instruction to uncheck “Enforce Host Tag Search for CFS” then put Outlook back to use HTTP first. No more warnings on the firewall, and Outlook started behaving.