My office just switched to Thunderbird from Outlook and we have multiple computers synced to view the emails. The problem I'm running into, though, is that I am not the only one checking emails, so if my coworker reads an email on her computer it is marked as unread for all the computers. This is a problem because then I don't know which emails I have not read yet. Outlook had one feature that I particularly liked: if my coworker read an email, it would show up as "unread" on all the computers but there would be a little envelope icon next to the email to show that my personal computer still had not read that email. Once I viewed the email, the icon would go away and it was easy to see which emails I still needed to attend to even if they showed as generally unread. Does Thunderbird have anything like this?? Maybe even in add-on form?