You appear to think someone here will be familiar with the way Eudora searched. Those folk do not exist here, so you need to explain what you think you want. However there is no general search based on the message headers in the global search. That is true. Just as there is not search in the message body source, only on the displayed information in the body. The global search uses a tokenized view of the information and manages numbers particularly badly and can not search on word of less that three characters at all as those are simply not indexed. You can use customized search fields in search (Ctrl+Shift+F) to search specific header fields but it is a per account search, but I would assume that searching header fields like the received header (which can appear multiple times) will function that same way as it will in filtering and only act on the first occurrence found. So it really would depend on what fields you were thinking should contain the senders IP address.