ISSUE: Email send/receive works from webmail but while accessing them from email client a popup box keep appearing for authentication.

Exim logs show:
fixed_login authenticator failed for (localhost) [127.0.0.1]:54412 I=[127.0.0.1]:25: 535 Incorrect authentication data
Tried following but did not fixed the issue:
/scripts/eximup – - force
/scripts/upcp
/scripts/mailperm
FIX that worked for me was:

Correcting ownership for etc directory under user.
Change ownership recursively for etc directory.
chown user.mail /home/user/etc -R
Note: Replace user with actual cPanel username.