Emails not sending from email address in email settings

[lubos]

There is another topic for this issue:

Emailing invoice error message

Hi all, I’m trying to email invoices out as I usually would, but the below error message comes up. I’ve tried updating to the latest version of the software but the issue still exists. System.Net.Mail.SmtpException: System.Net.Mail.SmtpException: Syntax error, command unrecognized. The server response was: 5.7.0 Mailgun is not loving your login or password at System.Net.Mail.RecipientCommand.CheckResponse(SmtpStatusCode statusCode, String response) at System.Net.Mail.SmtpTransport.SendMail(Ma…