External SMTP server setup
I am getting “Failed to send message: 221 … ESMTP server closing connection”
1). If you are using an ISP, please check its website for email configuration for email clients, such as Microsoft Outlook. Sometimes, your login name might be the name only, or firstname.lastname@example.org, or name%company.com.
2). Try to check “Secure Password” on and off to see which one works for your email server.
3). Sometimes your ISP might have port 25 blocking. You need to contact your ISP to unblock port 25 for you.