[Pkg-exim4-users] "no secret in database" messages

[Ross Boylan]

auth.log shows entries like
Aug 29 01:02:03 corn exim4: no secret in database
and
Aug 29 01:05:04 corn exim4: need authentication name
The former occurs repeatedly.  They occur in a burst a little after 1am,
another after 2am, and then nothing.

At the same time exim's logs show
2008-08-29 01:01:33 cram_md5_sasl_server authenticator failed for
114-44-141-95.dynamic.hinet.net (xnxvve.com) [114.44.141.95]: 553
Initial data not expected
2008-08-29 01:01:33 H=114-44-141-95.dynamic.hinet.net (xnxvve.com)
[114.44.141.95] F=<utpmsf at lexjll.com> rejected RCPT
<rwbhur2554 at yahoo.com.tw>: relay not permitted
2008-08-29 01:01:34 unexpected disconnection while reading SMTP command
from 114-44-141-95.dynamic.hinet.net (xnxvve.com) [114.44.141.95]
2008-08-29 01:01:35 cram_md5_sasl_server authenticator failed for
114-44-141-95.dynamic.hinet.net (mdcchpmfl.com) [114.44.141.95]: 535
Incorrect authentication data
and many more like that, with different domain names.

Can anyone help me understand what is going on, and if it's something I
should be concerned about?  I use authentication when I send mail up to
my smarthost, and I also encrypt connections inbound.  Originally I
thought the errors concerned one of those activities, but I suspect it's
something else.

Thanks.
Ross Boylan