Unable to connect to the MTA on fresh Carbonio install

On a fresh carbonio install, when trying to send email from webmail, it fails.

On checking the log file /opt/zextras/log/mailbox.log

tail -f /opt/zextras/log/mailbox.log

found following error message

com.zimbra.cs.mailbox.MailServiceException: try again: Unable to connect to the MTA

The error was because carbonio use invalid port for smtp:

zextras@mail:~$ zmprov gcf zimbraSmtpPort
zimbraSmtpPort: 20025
zextras@mail:~$ 

To fix it, set SMTP port to 25 with the command:

zmprov mcf  zimbraSmtpPort 25

After running the command, you can verify SMTP port is changed with the command:

zextras@mail:~$ zmprov gcf zimbraSmtpPort
zimbraSmtpPort: 25
zextras@mail:~$ 

Some useful symlinks

ln -s /opt/zextras/common/sbin/mailq /usr/local/bin/mailq
ln -s /opt/zextras/common/sbin/postqueue /usr/local/bin/postqueue
ln -s /opt/zextras/common/sbin/postcat /usr/local/bin/postcat
ln -s /opt/zextras/common/sbin/postsuper /usr/local/bin/postsuper

ufw firewall

ufw default deny incoming
ufw default allow outgoing
ufw allow 22/tcp
ufw allow 80/tcp
ufw allow 443/tcp
ufw allow 25/tcp
ufw allow 465/tcp
ufw allow 587/tcp
ufw allow 110/tcp
ufw allow 995/tcp
ufw allow 143/tcp
ufw allow 993/tcp
ufw allow 6071/tcp
ufw enable