Susan:
 
My feeling is if e-mail delivery of your digest to particular
users is unpredicatable and/or unreliable, then the user
should either: 1) switch service providors, and/or 2)
learn how to search the archives (assuming you have archives)
for particular items (alternatively GET the archive).
 
Logs may be maintained on an individual ("separate") message item
(NOT recommended) or weekly (and other longer frequencies).
 
For examples of "separate" take a look at the RISKS index and
HSPNET-L (massive).
 
Note that the "separate" numbering scheme may not be exactly
how you would like it (the low order digits are sequential,
but don't recycle at a year's boundary).
 
--  co-owner INFOSYS, TQM-L, CPARK-L, ERAPPA-L, JANITORS, LDBASE-L, et -L
URL:mailto:[log in to unmask]          "Kids: don't e-mail to strangers!"