[justsomehnguy]

base64 encoding does not include spaces and short strings are padded (and there is no '@' in RFC4648), so I wonder how this works too.

[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 ^