HI all, Im not completely sure if i understad it corecty how it works, so if someone could clarify it, it would be realy great. So lets just say this is the configuration. I got Outlook 2007 configured to use on fast networks TCP/IP first, and on slow networks HTTP first (and its a Exhcange 2007 organization). But how does Outlook know when to change and use RPC over HTTP instead of MAPI? Whats the mechanism how does it know? Tnx in advance!!!

Slow network is supposed to be <= 128 kbps, fast > 128 kbps. This was one of the algorithms that once were documented for at least Outlook 2003. But you will also notice that there are other algorithms. As we usually have to do with "fast" networks, Outlook tries first TCP/IP (MAPI RPC), if that fails, it will switch to RPC over HTTPS. You can see this with Network Monitor. While we're at it, I like the comment below very much: When Microsoft coded Outlook, they coded in some logic to cycle between the two connection types. If both fail, Outlook takes a deep breath and then tries the two protocols again. It is that deep breath in-between cycles that gets longer before trying the connection again. And before you ask... no, it isn't documented as far as I know. neo [mvp outlook] posted on Monday, June 23, 2008 6:29 PM http://www.eggheadcafe.com/conversation.aspx?messageid=32526443&threadid=32490414 Do also see the thread below with our problems from Singapore to Norway from some hotels: Sporadic Issue with Outlook Anywhere http://social.technet.microsoft.com/Forums/en-US/exchangesvrclients/thread/159d1a74-5828-422d-9522-e542b36c9db1MCTS: Messaging | MCSE: S+M | Small Business Specialist

Thanks Jon-Alfred, but how does outlook know that its supposed to use RPC over HTTP when i connect from a fast internet link, how does it check to that? tnx

Outlook does a DNS lookup for the local Exchange server and receives a DNS response Name error (the DNS server cannot find the Exchange server), then Outlook asks for the Outlook Anywhere URL and receives a DNS response Name success. Finally a SSL connection is established. Download Microsoft Network Monitor 3.4 to see this behavior http://www.microsoft.com/downloads/details.aspx?FamilyID=983B941D-06CB-4658-B7F6-3088333D062F&displaylang=en Problems arise if the DNS lookup for the local Exchange server does succeed and does not return a valid address. This was the case with a course center in Oslo and a hotel in Singapore. This is a non-standard DNS response modification which sees to be known by various labels: sub-domain redirection, NXDomain redirection, rewriting, hijacking ... a default IP address mapping for all not-found queried names in the DNS zone file, known as "wild card synthesis." In this case Outlook will not switch over to RPC over HTTPS, alt least not Outlook 2007 SP2, as far as we could tell. MCTS: Messaging | MCSE: S+M | Small Business Specialist

Tnx Jon-Alfred! i was reading a white paper about that but wasnt realy sure http://technet.microsoft.com/en-us/library/bb332063(EXCHG.80).aspx

Thanks for coming up with this question. Had almost forgotten. About a year ago I spent several days and nights pondering over the ins and outs of Outlook MAPI RPC and RPC over HTTPS. :-) MCTS: Messaging | MCSE: S+M | Small Business Specialist

Tnx for replaying and giving me links to these treads, yes i found it realy hard to find some documentation how it actually works from the client side. All the best!