Error! You cannot open more than 10 drafts at the same time

[overkilln99]

Can't reply to emails.
What's the fix?

[BruceW]

Look for a row of minimised rectangular "Compose" windows across the bottom of your email screen. Click each one to restore it, and then Send, Discard, or Discard/Save as Draft. See https://i.imgur.com/o2iGzRK.png.