You might want to check a previously received distribution from your list
at the AOL site.  Look at the RECEIVED line headers.  Reading them from
the bottom, up, look for the hostname that was "closest" to an AOL host
address.  This is probably the mailing transfer agent having problems
getting to AOL (possibly an anti-spam filter at AOL based upon any one of
a number of configuration options implemented by AOL).

/P