There are indeed various faults and delays in the network which introduce
delays in such  distributions. One of them is a  natural phenomenon known
as "IETF Conference". During an "IETF Conference", the network is totally
unusable due  to the combination  of a  physical phenomenon known  as the
"IETF Multicast",  which happens  whenever more than  a few  hundred IETF
people find  themselves concentrated  in the  same physical  location and
eats up all the available bandwidth in  the network, and of the fact that
the people  who would  know how  to fix such  problems are  attending the
conference and not available on site to fix problems. There are of course
other  sources of  problems. All  in all  your LISTSERV  log activity  is
likely to  fluctuate in the  same manner  as your sendmail  log activity.
There  is nothing  to worry  about unless  the blackouts  are very  long.
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  Eric