Thank you :-)
We are (mostly) python house on the back-end so I might use python instead of perl but I like the approach you suggested.
echo Z3JlZ0Bhc3NldG1hcHBpbmcuY29tCg== | docker run -i busybox base64 -d
>>> import base64
>>> email = "Z3JlZ0Bhc3NldG1hcHBpbmcuY29tCg=="
>>> print(base64.b64decode(email).decode('utf-8'))