I changed debuglevel to 1 and looked at the response on the recipient names. They are BOTH accepted, but still only my id (d123456) receives the e-mail. The long id (d1234567890) never gets the e-mail. Here is the excerpt of the exchange.
send: 'mail FROM:<[EMAIL PROTECTED]> size=160\r\n' reply: '250 2.1.0 <[EMAIL PROTECTED]>... Sender ok\r\n' reply: retcode (250); Msg: 2.1.0 <[EMAIL PROTECTED]>... Sender ok send: 'rcpt TO:<d123456>\r\n' reply: '250 2.1.5 <d123456>... Recipient ok\r\n' reply: retcode (250); Msg: 2.1.5 <d123456>... Recipient ok send: 'rcpt TO:<d1234567890>\r\n' reply: '250 2.1.5 <d1234567890>... Recipient ok\r\n' reply: retcode (250); Msg: 2.1.5 <d1234567890>... Recipient ok -- http://mail.python.org/mailman/listinfo/python-list