Bayern - E Overprint?

I think the postmark is Munich, but I don't know where the E came from. Any help please?

They needed some railroad postage marks(Eisenbahndienstmarken)
so they got out their big red stamp!
Scott O4 75CENTS

Thank you butterfly, tally it up at the end of the day and I will owe you. I appreciate it immensely. - Jeff

The true story on the big red E is rather complicated. There were two types of E.
You appear to have the thicker one. Forgeries also exist. Will edit later

Edit-- It looks like in 1908, the railroad officials lost their free mailing privileges, so this overprint was generated for their special use. This apparently allowed the government to determine the amount of mail being used this way. Later on E perfins were used.

cool, thanks butterfly

I found this one with a green E