Well, the first two things you should check: if your email client is configured incorrectly and if you have entered the domain name incorrectly when creating the virtual server.
Who, what, why, when and where are the things that should be stated explicitly in any communication, if they are not clear to all implicitly. I am unable to understand what you mean by “I have checked it everywhere but not found it.”
[root@webmail2 ~]# cat /etc/sysconfig/saslauthd
# Directory in which to place saslauthd's listening socket, pid file, and so
# on. This directory must already exist.
SOCKETDIR=/run/saslauthd
# Mechanism to use when checking passwords. Run "saslauthd -v" to get a list
# of which mechanism your installation was compiled with the ablity to use.
#MECH=pam
MECH="rimap -r"
# Additional flags to pass to saslauthd on the command line. See saslauthd(8)
# for the list of accepted flags.
#FLAGS="-r"
FLAGS = "-O webmail2.abc.in"
OPTIONS="-c -m /var/run/saslauthd -r"
PARAMS="-m /var/run/saslauthd -r"
[root@webmail2 ~]#
According to the docs I gave you, it’s not configured with the correct FLAGS, however I’m not 100% sure that’s applicable in newer versions (as I don’t use CentOS).
But I can add that I did a quick test myself and while logging in from an IMAP client like Thunderbird, or the app on my phone, it logs in as user@domain, whilst on RoundCube it shows user-domain.
Don’t know if that’s your issue though.
If installed with the install scripts, it seems RC is just looking at the usermap from /etc/postfix/virtual which also includes the user-domain users. If there’s any way to make RC make use of the user@ instead, I don’t know. Maybe ask @Joe
Different issue, please open a new thread for this.
Hint: include your /etc/postfix/main.cf right away.