CentOS 7 dovecot 2.2.10 postfix 2.10.1 squirrel web mail problems and solutions

problems and solutions:
# dovecot --version
2.2.10
# postconf -d | grep mail_version
mail_version = 2.10.1
milter_macro_v = $mail_name $mail_version
# uname -a
Linux xxxxxx 3.10.0-514.26.2.el7.x86_64 #1 SMP Tue Jul 4 15:04:05 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

1. can not login to squirrel web mail: permission denied
error connecting to IMAP server: localhost. 13 : Permission denied
setsebool -P httpd_can_network_connect on #save change permanent
2. squirrel web mail can not send/receive email:
Aug 2 16:19:49 localhost postfix/smtpd[5959]: warning: SASL: Connect to private/auth failed: No such file or directory
Aug 2 16:19:49 localhost postfix/smtpd[5959]: fatal: no SASL authentication mechanisms

find this part(it is include in "service auth" block) in /etc/dovecot/conf.d/10-master.conf , uncomment the lines and change to the following.

unix_listener /var/spool/postfix/private/auth {
mode = 0666
user = postfix
group = postfix
}

in /etc/dovecot/conf.d/10-auth.conf:
change "auth_mechanisms = plain" to "auth_mechanisms = plain login external", to support SASL, we need to add external to supported auth_mechanisms

then restart dovecot: systemctl restart dovecot
3. still can not receive email to info@tradebay.ca:
in /etc/aliases

change "info: postmaster" to "info: info", then restart dovecot: systemctl restart dovecot