Right smack in the middle of the "Dr.-Livingstone,-I-presume?" era of British adventurism in Africa, a journal belonging to William Simposon was published, titled Private Journal Kept During the Niger Expedition of May 1841 to June 1842.
In the introduction it states that Simpson "obtained Bibles and different religious publications for distribution, and at the suggestion of some Christian friends, he was provided by the two chief Rabbis in London with letters commendatory to their brethren, in case it should be found that in the providence of God toward that remarkable people, any portion of them were located in the interior of Africa."
This is quite interesting, because Simpson was clearly a Christian missionary. Yet at least Rabbi Solomon Hirschell was convinced that he did not proselytize to Jews, and with such full confidence sent his greetings to any Jews that Simpson might encounter. David Meldola, acting Haham of the Sephardim, sent his greetings as well. The text of these letters along with an iffy translation were included in an appendix to the book. Note that Rabbi Hirschell's letter was not written by him, but on his behalf by Aaron Levy of Lissa, a dayan on his bet din, who repeated twice that Simpson is not מבני עמינו - but he is an אוהב ישראל, a philo-semite. And check out Meldola's pledging allegiance to the Rambam, not the Shulchan Aruch: