Email from PMAIL support after review of log files I provided. Appears that Eaarthlink has made a change:

 Ok here is the problem. It appears this is one of the servers that advertise the

AUTH type CRAM-MD5 but have not really implemented it. This is why David added the option

in v4.6x to "Do not use CRAM-MD5 authentication even if it is advertised " If you select this

option when editing the SMTP setup under "Security" then it will fall back to using the AUTH

PLAIN or LOGIN.

Selecting this option does fix the issue. I have provided this feedback to Earthlink as well.

Sometime overnight all 3 of the computers at our house stopped sending email. After lots problem solving and talking to Earthlink Tech Support, (who told me to use Outlook) I believe I have found a work around.

This morning if I wrote a single email and then sent it, it would fail with an authentication error. I then noticed that if I had BCC'd somebody, the BCC email went. If I wrote 5 emails and then tried to send, the first one would fail, but the next 4 would work.

 I ended up changing the smtp definition to do a login prior to sending mail (previously I simply gave it the credentials to use - has worked that way for 5 years)

 It now works but thought others may run into this and wanted to share.