Message read setting.

[Lady in France]

Although I have set the message read to show after 25 seconds the moment
emails are downloaded the envelope is open and looks like it is read. Today
25 messages came in, at once they all showed as read and the white envelope
showed. I know the yellow envelope should show till messages actually read.

 

[mac]

Although I have set the message read to show after 25 seconds the moment
emails are downloaded the envelope is open and looks like it is read.
Today
25 messages came in, at once they all showed as read and the white
envelope
showed. I know the yellow envelope should show till messages actually
read.

I have the read time set to 0 (zero) seconds.

That setting does NOT cause what you appear to be seeing.

Most likely you have a message rule set up that affects all mail, and is
marking them as read?
Tools>message rules>mail.