WowAce

I am also curious if there is any plans to port this over for Classic WoW. I was able to get the most recent version to work simply by modifying the postal.toc file a little. I changed the Interface and version numbers at the top (which I think are commented out anyway so not sure this did anything useful) as well as I commented out the "Modules\Blackbook.lua" line and hit save. I only commented out the Blackbook because I logged into Classic and as soon as I opened the mailbox and clicked the dropdown arrow to find a name, it popped up a lua error regarding Blackbook.lua I should be able to reproduce the error and post it here if anybody is actually planning on working on a classic version.

P.S.- When I say "commented out" that means adding "##" to the beginning of the line of text.

OK, tried and working:
On Modules\Blackbook.lua line 358, I edited like this:

function Postal_BlackBook:SortAndCountNumFriends()
	wipe(sorttable)
	local numFriends = 0
--	local numFriends = GetNumFriends()
--	for i = 1, numFriends do
--		sorttable[i] = GetFriendInfo(i)
--	end

 Since only the function GetNumFriends() is not working, i replaced it with 0 (it still look for bnet friends after)

Removed all the changes I had made to both postal.toc as well as blackbook.lua and modified Blackbook.lua like Atrealis mentioned.

At Blackbook.lua line 358 I have:

function Postal_BlackBook:SortAndCountNumFriends()
      wipe(sorttable)
       local numFriends = 0
--    local numFriends = GetNumFriends()
      for i = 1, numFriends do
             sorttable[i] = GetFriendInfo(i)
end

This allows Postal to work as intended. It will get your friends, local alts, account alts, guild members and not yell obscenities at you. Thanks Atrealis, yours was a much simpler way to do it than what I originally did. /cheers

Found! you need to replace GetNumFriends() by C_FriendList.GetNumFriends() (Thanks Meorawr) so it makes:

local numFriends = C_FriendList.GetNumFriends()

There's a packaged addon with little more changes there: https://git.dess.ga/Albirew/Postal/releases/latest

This seems like such a simple fix, why not bit the bullet and push a classic version? Please? It's been 18 months. I've been using the version from https://www.wowinterface.com/downloads/info25366-Postal_Classic.html since it was posted and it works wonderfully. The only issue is it doesn't auto collect AH gold mails.No errors, it finds my alts, guildies, recent addressees, etc. It's not like classic is going away, and there will be even more people that could benefit in TBC classic.

Can a few people try the following alpha on Classic.  I don't play Classic myself, but I believe these changes should work.  Thanks!  Please leave feedback on this thread.  You will need to check on load outdated Addon's for this to work.

https://www.curseforge.com/wow/addons/postal/files/3246779

Done!