After sites migrations from one server to another we have a problem with this error: 550 Bad HELO - Host impersonating domain name [] in line 457 of AbstractSmtpTransport.php file. This error occurs when I try to send test mail in administration panel (Settings > Mail > Mail templates > my template) and from my site via contact form. I am using PHP mail method to send messages. I have read that is caused by duplicate information after site migration and I have to delete all traces from the previous server. However, I don't know where to find this traces.

I found solution to add this to config of phpmailer, $mail->Hostname = ""; $mail->Helo = $mail->Hostname; but I don't know where, how to add it and how it works.

Maybe one of you was struggling with a similar problem and knows how to deal with it?

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