I think current telegraph/electricity poles are "european redwood" aka scots pine? Which is then obviously treated with creosote.
If you go down a builders merchant and ask for treated timber usually all they will have is cheap pine/spruce that is dipped with some watery junk that doesn't do much to the life of the timber.
You can get other more durable species from a good timber yard or sawmill. Larch, chestnut etc
The old fenceposts round here are Larch (heartwood) and they have lasted 40yrs or whatever, and they are only 3" thick.
Some places also sell creosote treated posts/rails etc
Coal tar creosote is available to buy in a minimum of 20l drums for "professional use only"
I don't think placing a timber post in concrete helps either. Rammed earth is fine.