Unable to send emails via mail client with the smtp 587 port configured.
When the option Tools & Settings > Mail Server Settings > Enable SMTP service on port 587 on all IP addresses is disabled, the service is not used and thus port is not opened.
If it is required, open port 587 by following the next steps
Go to Tools & Settings > Mail Server Settings.
Turn on the Enable SMTP service on port 587 on all IP addresses directive and press the OK button.