Sending e-mail with earthlink

I am trying to set up Evolution with my earthlink account. I have no problem receiving e-mail, but sending does not work. I get an error message:

Error while performing operation.
RCPT TO<SMTP> failed: Syntax error in parameters or arguments

Earthlink requires authentication, and it uses port 587 for the smtp server. My settings are:

Server Type: SMTP
Server: smtp.earthlink.net:587
Security No Encryption
Authentication Type: Plain

If I "Check for Supported Types" of Authentication it gives me the option of Plain, CRAM-MD5, and Login for both "No Encryption" and "TLS encryption". If I "Check for Supported Types" with SSL Encryption I get an error

Error while Checking Service.
Welcome response error: Input/output error

I believe I have tried all supported combinations of Security and Authentication, and all seem to give me the error:

Error while performing operation.
RCPT TO<SMTP> failed: Syntax error in parameters or arguments

when performing send/receive

Thanks for your help!

Dave C