I send an email.  Reply from the person doesn’t come into my “inbox” - it stays attached to the original email in the “sent” folder.  If I’m not sitting at my desk to see the popup for the new mail, I’ll never know I have a reply to that original email.  How do I change this.  It just recently started happening (as far as I know - but maybe I’ve missed more email replies than I know !).   PS  I am using Gmail and Yahoo.  To further complicate this, I sent myself a test email from Yahoo to Gmail – the sent mail folder in Yahoo shows the sent mail – but the email never comes into the Gmail Inbox !  Help ?  

Hello Carol,
is this perhaps just a confusion caused by the Conversations feature? Try disabling Conversations in Menu>View>Conversations and see if the messages show in their proper folders.

If not, please check if there are any rules in Menu>Tools>Rules that could cause this.
If that is not helpful either, please take a screenshot of your IMAP settings for the affected account in Menu>Tools>Accounts. I need to see the Special folders settings.