Are these just aliases that will forward to your email mailbox or are you setting up 50 individual users with their own passwords?
If it's the first one with email@example.com firstname.lastname@example.org forwarded to email@example.com then you can use the bulk forwarding option here
I added 30 recently but used windows notepad
abc qq zz
def qq zz
sales qq BOUNCE
info qq DELETE
Then used the replace feature to replace qq with the @domain name and zz with the mbx name before pasting it into the control panel. It saves wearing out the fingers.
If it's 50 individuals then I don't think there is a way other than using the control panel one by one.