I am using El Capitan (.6) as well and when I use Mail, I have it open full screen in its' own space. I have the View set up with my Mailboxes in the "sidebar", then the Email list, sorted by date. In this column, along the left, I have my reply/forward/attachment/blue dot icons showing, and the last section is where the email is displayed.
So is it fixed? You said in post # 12 "
I am staring at 8 emails that I have responded to and each one shows a "reply" arrow next to it on the left." What is the date these emails are from? The last time I replied to an email was 8/26 and it has the reply icon with it. Is there a date that you are positive this started?
Can you compare, the last time that it happened that the icon did not show up, the email you received and the email you sent, can you confirm the "sent from" email address is the same as your "received" email address?
For example, you received an email at
[email protected], but it sent from your
[email protected], by accident. Maybe when you sent it, that server was busy, and it sent from a different "of your accounts" server?