Mark a Conversation or Individual Emails Unread in Gmail

In the middle of an email thread, it's awkward to stop responding. If you're just glancing at a Gmail conversation and don't have time to respond, you'll want to keep that particular message in the thread in mind and visible in Gmail so you can continue reading later.

You can mark the email unread, of course, or star it perhaps—or rely on a hidden Gmail gem that lets you mark a thread unread only from a certain message onward.

Mark Individual Emails Unread in Gmail

To mark an individual email message unread in Gmail, do the following:

Make sure conversation view is disabled. To disable conversation view, select the Settings gear icon at the top right corner of Gmail. Then, choose Settings in the menu that comes up
Go to the General tab.
Under the Conversation view section, select Conversation view off.
Scroll to the bottom of the page, and press Save Changes.
Find and check or open the desired email.
Press More in the toolbar on the right side of the window.
Select Mark as unread.

Mark Part of a Conversation Unread in Gmail

To mark as unread only part of a thread or just the latest message in Gmail:

Open the conversation in Gmail.
Make sure the message in the thread that you want to mark unread is expanded.
If you cannot see the message, select its sender's name and preview.
You can also select Expand all to the right of the thread.
Select More denoted by 3 vertical dots next to Reply in the message's header area.
Select Mark unread from here from the menu.

You can also mark the entire thread unread, of course, by expanding it and selecting the More button in the toolbar. Select Mark as unread to mark the entire thread as unread.