If you are unable to send emails from your server, it is possible that your server IP address(es) have been listed in public spam blacklists.You can check your IP status using online tools, such as MxToolbox - https://mxtoolbox.com/blacklists.aspx If your IP is not listed, check if connection to remote servers is working by issuing following command via shell:
telnet smtp.gmail.com 25
If connection to remote server fails then check firewall settings and look if you got any notifications to your registration email address regarding IP being limited due to spam risk. Mail filtering system could block port 25 for your IP. To confirm whether this is true please check the inbox of email address which is tied with your Heficed account for the notification about temporary blocked IP address. These notifications are being sent automatically once mailing activity triggers Heficed anti-spam rules.
This can happen due to various reasons: misconfigured mail service on your server, bulk email sending, low quality email content etc.
Our recommendations for email sending:
600 emails per hour (120 emails per minute) for VPS and Cloud services;
emails should not contain large attachments;
emails should not contain suspicious code;
emails should not contain spam-like content;
advertisement emails should contain an unsubscribe option;
After you made the suggested modification to your mail service, email content and cleared your mail queue, submit a ticket to our Support and request to unblock your IP.
Please note that it is strictly forbidden to send spam messages from our servers.
You can read our terms of service here.