User-Agent: Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.8.0.7) Gecko/20060909 Firefox/1.5.0.7 Build Identifier: Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.8.0.7) Gecko/20060909 Firefox/1.5.0.7 When Thunderbird is chosen as the preferred mail client, it replaces the existing c:\windows\system\mapi32.dll with its own supplied version. This causes a third-party application to report: Error starting program. The OUTLLIB.DLL file is linked to missing export MAPI32.DLL:36 Reverting the mapi32.dll file to the original (which Thunderbird gracefully backs up) solves the problem for the third-party application, but then Thunderbird is no longer the preferred mail client, and the prompt to select that reappears when Thunderbird is started. Original Mapi32.dll: 716,048 bytes 06 Aug 97 Thunderbird's Mapi32.dll: 6,265 bytes 18 Sep 06 It would seem the third-party application relies on some functionality present in the original Mapi32.dll, but absent in Thunderbird's Mapi32.dll. Reproducible: Always Steps to Reproduce: 1. Install Thunderbird 2. Select as preferred mail client 3. Start third-party application Actual Results: Third-party application reports an error in starting program: The OUTLLIB.DLL file is linked to missing MAPI32.DLL:36 Expected Results: Third-party application should have been unaffected by the switch of mail client (from Eudora to Thunderbird, as it happens) Original Mapi32.dll is reported by explorer as: Comments: Service Pack 1 Company Name: Microsoft Corporation Internal Name: English (United States) Legal Trademarks: Microsoft® and Windows® are registered trademarks of Microsoft Corporation. Original Filename: MAPI32.DLL Product Name: Microsoft Exchange Product Version: 5.0