My ISP, Virgin Media, uses Google Apps to provide email service, and they appear to require SMTP authentication. Here is
the information and
some more information. My impression is that this is pretty normal, at least in the UK, and has been for about 5 - 10 years.
Having said which, I have tried putting my ISP's SMTP server in the relevant box in MinePeon, and haven't yet bothered unplugging the Butterfly miner to see if it works without a password.
I have now successfully received some emails from the Peon, so disregard the above. On the other hand, Gmail put them in my spam folder, and SMTP Auth might help with that. Actually, now that I look more closely, the email appears to have no 'To:' address, as if it's been BCC'ed - possibly it would help to fill that in? Perhaps this is because I entered into the Peon control panel the from address where the to address should be? I wasn't sure what should go in the box, because it just says 'email address' and not 'from' or 'to'. I think my ISP forces the from address to be a particular thing, so perhaps the 'to' address has been dropped by being the same.