After upgrade to El capitan native mail keeps asking
for the password but says its incorect, the funny thing
is mail is working can receive send.
Also OSX is latest version.
This has been a problem for a number of users with every version of Apple's Mail for years now. It isn't at all uncommon. I'm not sure that Apple can easily fix the problem, because part of the problem is with your ISP.
It is due to a timing issue between Mail and certain ISP's. Mail gives your account password before your ISP's
server is ready for it. When the server is finally ready for it, the
password has already been given, and the server waits, times out, and then requests the password again or says that it hasn't been given the correct password.
I had previously worked out a solution to the problem using Access Control in the Keychain application that worked in most cases. Unfortunately, Apple changed things in the Keychain in El Capitan, and the settings to fix the problem don't seem to exist anymore. (Here is the old solution if anyone wants to try and hunt down the settings and see if they exist somewhere else in El Capitan.)
Launch the Keychain application, located in your Utilities
folder.
in the Edit menu, choose Keychain List. Now in the Shared column check both System and Login.
In the upper left column, highlight Login.
In the lower left column, highlight Passwords.
In the right window scroll until
you find your internet service provider's incoming and outgoing mail servers.
They are usually called something like:
"mail.yourisp.com"
and
"smtp.yourisp.com"
For Comcast they are:
"mail.comcast.net"
and
"smtp.comcast.net"
Double-clicking on each (in turn) will bring up a window with tabs at the top
which say Attributes and Access Control.
Select Access Control.
Then select "Allow all applications to access this item." Make sure you do this for both
the incoming server and outgoing server keychain items.
If the above turns out to be a dead end for you, this article may provide a solution:
http://www.macissues.com/2015/07/08/manage-os-x-always-asking-to-use-your-keychain-passwords/