Decrypt SHA1 Base64 Hash

After spending a good hour searching I came across an article that explained that you can’t reverse a hash value. How true is this? I need to reverse a base64 encoded Sha-1 email address but I can’t seem to find a way without knowing what function was used to hash. Or is there an easier way of going about this?

SHA1 is a one-way algorithm or one-way encryption. Theoretically, the only way to ‘decrypt’ this is to take known plaintext, hash it, then compare it to the hash value you have.