![]() The “Via” header indicates presence of a proxy between client and server. While the headers gives you idea of what in included in a normal POST request from the client, for me, the first and last headers were very important. Here’s the most relevant piece of data from the trace file (I have removed unnecessary headers for brevity): When the error occurred, numerous xml files were created by IIS. MAC MAIL EXCHANGE SERVER NOT RESPONDING MACNow that the trace is enabled and rule configured to capture HTTP 400 error condition, I launched Mac Mail client and reproduced the issue. I had it configured this way only for troubleshooting purpose in my lab and no production data was in flight during testing. I don’t recommend this configuration in production and KEMP LoadMaster default setup uses more secure ciphers. I was able to decrypt client side traffic due to load balancer configuration of ciphers that didn’t use PFS. ![]() Due to newer ciphers which use PFS (Perfect Forward Secrecy) I couldn’t decrypt data being received from load balancer by the server despite having the private key used to encrypt the information. I needed to correlate this with the data being received on the Exchange server. The response included data that was requested by POST operation. Notice how the pattern looks similar to Mac Mail’s second POST request, however, it ends with 200 OK. POST /ews/exchange.asmx 401 Unauthorized POST /ews/exchange.asmx 401 Unauthorized POST /ews/exchange.asmx 200 OK When comparing that with Outlook for Mac, the pattern looked like the following: However, this time the pattern followed multiple 401 responses from server and ended with 400. At this point Mac Mail client started with another POST operation to EWS. Notice how initial dialog included challenge response for NTLM authentication and ended with 200 OK. POST /ews/exchange.asmx 401 Unauthorized POST /ews/exchange.asmx 401 Unauthorized POST /ews/exchange.asmx 400 Bad Request POST /ews/exchange.asmx 401 Unauthorized POST /ews/exchange.asmx 200 OK Looking at the trace captured using Wireshark on the client machine, I noticed the following HTTP dialog: MAC MAIL EXCHANGE SERVER NOT RESPONDING FOR MACMicrosoft Outlook for Mac did not have issue connecting to Exchange even before we changed 100-continue handling to be RFC-7231 compliant.Īt this point, I decided to look at the network trace. Since we addressed the 100-continue handling in Part 1 of this article, ExRCA tests did not indicate any more issues. Let’s see what we can do to get the Mac Mail to connect successfully to Exchange servers.
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