I think I have at least a lead on the issue.  This is actually a client that I am doing some IT work for and it turns out they recently switched from one ISP to another.  The Axosoft installation was trying to send email out through an account (which still exists) at the old ISP, but is doing so through the new ISP's network.  Thus, the old ISP is rejecting the send request as unauthorized.  Since I did not have any login info for the new ISP, I just put in the full credentials for the old one and that seems to have fixed the problem.   

So, the answer to your question is: No, it did not require authentication in the past, but Yes, now it does (if I want to use the same sonic.net account).

P.S.  Before anyone pipes up, yes, I will switch to an account at the new ISP as soon as I get the information from the client.

P.P.S. Please considered this a bug report/feature request to provide better error reporting for this condition.

Thanks,
Dave Parker
IT SystemWorks