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Quickbooks and Thunderbird
Quickbooks only supports a few email clients, so if you are to install a 2nd one alongside an existing setup (Outlook), do not choose Thunderbird. Use something obscure. If you choose Thunderbird, when you already have Outlook setup, it is possible that Thunderbird will take over the email settings, and if you try to uninstall TB, everything in QB breaks. So stick with Claws or something less known, and don't mess with Thunderbird and QB, unless its the only email program you plan to use.
Outlook not visible in QB 2014 Send Forms after Thunderbird install
am running QB 2015, Windows 10 and Office 365 (x64). I tried most of the suggestions above but they did not work. What did fix it was changing this registry entry: \HKEY_CURRENT_USER\Software\Clients\Mail?. I set ?Microsoft Outlook? as the default. It was incorrectly set to Thunderbird. Reply ? Josh Kantro January 30, 2020 at 11:50 am I am running Quickbooks 2015 and Outlook (Office 365). None of the fixes worked for me until I made the following registry change. Check registry key: HKEY_CURRENT_USER\Software\Clients\Mail ?Start? > Run > type regedit Locate this registry entry: HKEY_CURRENT_USER\Software\Clients\Mail on right side double click on ?Default? Enter Microsoft Outlook in ?Value Data? Mine was set to Thunderbird and once I changed the value to Outlook I could see Outlook as an option in Quickbooks.