I can´t really find functionality how redirect e-mail with original sender.

For example, I received e-mail from address
google@google.com to my address person@company.cz
I can see it in my mail box as sender from google@google.com

For example this message I want to postpone to colleague@company.cz
If I use your functionality Forward as original in your program EM client, my colleague received original e-mail but as sender is my e-mail address person@company.cz instead original google@google.com.

And if he clicks to the button answer, it will be answer not to original address google@google.com, but to my address person@company.cz.

It always looks like forward and not real full redirect with original sender.
Exist some addons like for Thunderbird or possibilities how really redirect original message?

Minimally I don´t understand why you havn´t part (reply to) with pre-filled with the address of the original sender.
You have this information inside original message, so you can use it and if you can´t change real sender you can change the e-mail address for replay. See please my attached file.

If I use your functionality forward as attachment, you add it as attached file, recipient must open attached file, WHY this additional step, because you can´t directly open and show EML files :-(

So if you add possibilities show directly EML file and reply to, it can be great.