My problem is the same as written above
Since it is your post I would not have expected the issue to be different.
The latest is 8 versions newer than yours and is numbered 061.121.226.12400 and dated 06/16. Yours is dated 11/14.
The version you have will certainly have a plethora of issues due to the recently implemented SHA-2 encryption by the big dogs in SMTP (Gmail, Yahoo, Office365, AT&T, GoDaddy)
You already stated you know you are on older firmware and stated that email is working fine so my question still stands. You need to clarify what you are looking for with this statement because it makes no sense in the context of your post.
So I would like to know how I can obtain one because the problem bothers a lot.
Are you looking for a patch to enable some advanced at the time version of SMB? Because, again, your subject line implies you are looking for an email fix, and the The Solution portion of your post firmly states that is actually working fine.
The only SMB patch for version 3 SMB on 2012 dealt with remote directory lock errors, but the patch was designed specifically for versions of spars that are 5-12 versions older than the General release you are running, so no guarantees there.