Group Notices not reaching offline members

It appears to me that some group notices I send are not reaching members who are offline. Members used to receive my notices as soon as they logged on, but it seems that this no longer happens. Is there some setting that I have to use, or is this a bug?

Group notices can sometimes be spotty, but also, if the person in question gets a lot of offline IMs, their IMs can get capped, as there is a limit to how many SL will save. Group notices are considered in this count, as are group invites and on some occasions receiving items (although this seems to have improved a lot, lately I seem to get the item even if the notice about it was capped).