We moved a customer from BPOS (Telstra Hosted Exchange) to our own managed exchange. After hours of backing up mail boxes and restoring (due to the bpos platform being slow) and reseting up the profiles on the local pc i found the autodiscover kept prompting for a username and password for the bpos servers. (red003.mail.apac.microsoftonline.com) after some looking i found this link Revert Autodiscover Changes for Exchange Online
It has these steps
To revert Autodiscover changes for Exchange Online
Click Start, and then click Run.
In the Run dialog box, type regedit, and then click OK.
In Registry Editor, go to the following registry key:
Delete the following Autodiscover entries:
Exit Registry Editor.
Restart Windows for the changes to take effect.
After doing all this it still didn’t work. Same problem. Then after looking at the reg files that that BPOS installer runs i found that it puts a entry in
HKEY_CURRENT_USERSoftwareMicrosoftOffice12.0OutlookAutoDiscoverdomainname = =”C:DOCUME~1…outlook-autodiscovery.xml” remove this reboot and everything should be good to go.
you can also clean up the C:Users%username%AppDataLocalMicrosoftSign InConfigusername@domain
If you have issues with not being able to send to internal email’s try outlook /cleanautocompletecache