"I am sending mom's email."

Translation: Ninatuma barua pepe ya mama.

[nootheguru]

Ive never heard barua pepe before - Is this the usual way swahili speakers say email?

[machieng]

yes. 'Barua' is a letter/mail, 'barua pepe' is 'electronic mail' i.e. email

[SimonWerman]

Is there a way to know that this takes "ya" other than because it's in this lesson? Neither barua nor pepe looks line an n- noun.

[machieng]

I mean...that's the whole reason - because barua is in the N/N noun class. Nouns in the N/N noun class have no pattern anyway e.g. kalamu, nyumba, meza etc (also, 'pepe' is not an adjective, not a noun). Practice will help you learn to identify nouns and the noun classes, but some of them just don't have easily identifiable patterns