/ma/ is a humble term, but with a lot of meanigs int it!
In exclamations it carries meanings of different shades, as some of the following examples might show you.
Esiste un contesto esclamativo, in cui puoi usare soltanto /ma/.
Esempi:
a) ma che me ne importa! (I don't care about it!)
b) ma mi fai capire cosa vuoi da me ?
(here /ma/ means a mood of exasperation)
Let me understand what you want from me!
c) ma si`, e` proprio come ti ho detto.
(meaning of /ma/: emphasis of stating the truth)
d) ma pensi di poter comprare la mia amicizia ? (Do you really think you could buy my friendship ?)
Here /ma/ has a meaning of: negative surprise + reproach
Is there such a particle in the English language?, which btw I love very much .
Here