Learn English – What does “pass it” mean

I don't know the song, but pass it on normally means to share something with another or others, whether keeping it for oneself also or not, especially something received from a third party. Thus, for example, if someone smiles at you or greets you, you could be said to be passing it on if you smile at or greet someone else. If someone gives you a platter of chicken, you can take one piece for your plate and pass the platter on to the next person.

This usage of "if nothing else" is idiomatic, as D_Bye pointed out. In your example "... automated scanning, which every e-mail provider does, for security purposes if nothing else.", you could replace it with "if for no other purpose". It means that e-mail providers feel that security purposes are enough reason for scanning e-mails: they would scan e-mails for that reason alone anyway, so it doesn't really matter whether scanning could be justified based on other reasons.

A: Should I take some money from the company's cash box? Any reason not to?

B: Huh? What!? You might consider the possibility of getting caught, if nothing else [ = if you will consider nothing else].

B means that if A won't consider other reasons, such as the moral obligation not to steal, at least she should consider that she may get caught.