501 error Unexpected response from SMTP server during FROM address

[Sevo]

I am having this error when I am running diagnostics on my email. The server is not seeing emails.

This is the exact error

"Warning: 501 Unexpected response from SMTP server during handshake in [path]\includes\class_mail.php on line 586"

I found this thread https://vborg.vbsupport.ru/showthread.php?t=182310

Here is his fix

I wrote an app in c# that caught the error.

There was an extra Mailto: in front of the sender name of the email. I found it in the code of the Site Name / URL / Contact Details. the line that matches up with the "Contact us Link" form field.

Thanks everyone, a lesson learned. That error number means that the send name is not in the proper or acceptable format for the mail server to read. It can connect but not send because the From name format is not known.

my question is where do I find the php files that contains the sitename/url/contact so I can look at the code?

Thanks for the help