kama unatumia gmail basi nenda kwenye settings located in your upper right hand side...then ukishaclick hapo utaona kwenye tab ya general kuna Email signatures....chagua hapo then uandike details zako ambazo zitakuwa appended automatically for every outgoing email.
Si mtumiaji sana wa Yahoo so am not deep in it...labda nichimbue zaidi nayo...