Mozilla Thunderbird is a free, open source, cross-platform email, news, and chat client developed by the Mozilla Foundation and Microsoft Outlook is a personal information manager from Microsoft, available as a part of the Microsoft Office suite. Follow the guides below to configure your email account created using Webuzo : 1) Mozilla Thunderbird 2) Microsoft Outlook If at all you face a "550 Relay not permitted error" or "Authentication Error", the steps below will fix them all. Note : This Fix is applicable for CentOS 6.x Exim Configurations Open the Exim configuration using your favorite editor 1) auth_advertise_hosts vi /etc/exim/exim.conf Replace the line auth_advertise_hosts = by auth_advertise_hosts = * 2) Enable Authenticators Add the following right after "begin authenticators" begin authenticators dovecot_login: driver = dovecot public_name = LOGIN server_socket = /var/run/dovecot/auth-client # server_set_id = $auth1 server_mail_auth_condition = false dovecot_plain: driver = dovecot public_name = PLAIN server_socket = /var/run/dovecot/auth-client # server_set_id = $auth1 server_mail_auth_condition = false Save and file and Exim is all ready to be used. Dovecot Configurations 1) Edit the file 10-auth.conf using your favorite editor. vi /etc/dovecot/conf.d/10-auth.conf Replace the line auth_mechanisms = plain by auth_mechanisms = plain login Save the file. 2) Edit the file 10-master.conf using your favorite editor. vi /etc/dovecot/conf.d/10-master.conf Replace the following unix_listener auth-userdb { #mode = 0600 #user = #group = } by #unix_listener auth-userdb { #mode = 0600 #user = #group = #} unix_listener auth-client { mode = 0666 } Save the file. That's it !!! Restart the Exim and Dovecot services root > service dovecot restart root > service exim restart Support : https://www.softaculous.com/support/open.php?