[taneliv]

Could be one of the sibling encodings, like base85 or uuencoded, perhaps? From afar they could look sufficiently similar to base64 that OP got them mixed up?

[justsomehnguy]

There are some encodings with @, but the problem is why it would trigger notification in

  aslkdjfhkj@tanelivasdklfjhasdfasdfasd

or in, the best case:

  faskjdhgfkajshdgfasldfhaksdjf@taneliv

In both cases there are something before @ and it's not \s or ^