That suggests to me that your operating system's "default email client" has been reset and it no longer knows to pass these pictures to Thunderbird. So instead it tries to use whatever Microsoft would have chosen as the default email client, and that program hasn't been configured with your accounts. I suggest you go to your Windows Settings panel and search for the options for "default apps", particularly the one for email. I tend not to rely on these configuration settings. I'd just start a new email message in Thunderbird and add pictures to it. You should be able to view your pictures in your usual way and drag-and-drop them into Thunderbird. If you drop them into the message they will be embedded inline, that is mingled in with the message text . To send them as attachments, drop them onto the addressing box in your Thunderbird message. Alternatively, in Thunderbird, use the attach button on your toolbar or the attach option in your menu to send as attachments, or use the toolbar or menu options to insert an image to send it inline. Speaking as a user who switches between Windows and Linux, I'm more interested in using a generalised procedure that always works than a specific shortcut for one operating system. I don't use Outlook very often but every time I do, despite the settings expressly forbidding this, it sets itself as the system default email client. I know this has happened because when I next start Thunderbird I am asked if I want Thunderbird to be my default. You may have inadvertently done something similar and woken up your system's default email client.