Hi hughesmichele,
You’re right to suspect the New Outlook. There are known compatibility issues between New Outlook for Windows and AccountRight’s email functions. If you’re sending emails via Outlook (instead of using AccountRight’s built‑in email feature), you’ll need to use Classic Outlook, as New Outlook isn’t currently supported.
To switch back to Classic Outlook, in the top-right corner of the Outlook window, find the toggle that says New Outlook or Try the New Outlook and disable the toggle (slide it off). You might see a message that says Switching will restart Outlook. Now click Switch to revert to Classic Outlook. Once Classic Outlook reopens, try resending the email from AccountRight.
More information can be found on this help page Email troubleshooting then navigate to the section "I'm getting an error about Unsupported Outlook Version"
Regards,
Earl
