When connected to BlackVPN you can only send email with SMTP/ESMTP on port 465 and port 587. Port 25 is blocked due to spammers.

Sending email with SMTP/ESMTP is only allowed for certain domains (such as smtp.gmail.com, smtp-mail.outlook.com, smtp.mail.yahoo.com, etc). If you find that your email service is still blocked then please contact our support staff and we will add your email service to the white-list of allowed domains.