Roundcube not sending mails

You will get the following error while sending email from rouncube.

SMTP Error: SMTP error: Connection failed: Failed to connect socket: Connection timed out in /usr/local/cpanel/base/3rdparty/roundcube/program/steps/mail/func.inc on line 1418

It happens if you have CSF firewall installed and it is upgraded automatically or something like that. Just make following changes in to firewall configuration and it will fix the issue

nano /etc/csf/csf.conf
and search for 
SMTP_ALLOWLOCAL = 1 
Replace it with 
SMTP_ALLOWLOCAL = 0

It will fix the issue.