mailboxes

Dear users,

I'm very new in programming SystemVerilog and hope, you can help me.

I just wanna use a mailbox inside a class and have written the following code:

class test;

.................

mailbox mbx_get;                           // mbx_get: layer gets data, mbx_put: layer sends data, mbx_int1 and mbx_int2: intern mailbox
mailbox mbx_put;
mailbox mbx_int1;
mailbox mbx_int2;
 
mbx_int1 = new;                           // mbx_int1: send (intern) from attach_header() to snd_pkt_phy()
mbx_int2 = new;                           // mbx_int2: send (intern) from receive_pkt_phy() to remove_header()


// Code

endclass : test


Note: class declaration is inside a program block.
Trying to compile this code fails with the error message (there are more, but these are the first:

ncvlog: *E,NOIPRT (class_layer2.sv,25|8): Unrecognized declaration 'mailbox' [SystemVerilog].
  mailbox mbx_put;
        |
ncvlog: *E,NOIPRT (class_layer2.sv,26|8): Unrecognized declaration 'mailbox' [SystemVerilog].
  mailbox mbx_int1;
        |
ncvlog: *E,NOIPRT (class_layer2.sv,27|8): Unrecognized declaration 'mailbox' [SystemVerilog].
  mailbox mbx_int2;
        |
ncvlog: *E,NOIPRT (class_layer2.sv,28|8): Unrecognized declaration 'mailbox' [SystemVerilog].


Can you tell me what to to. Searching by google just give me one hit and so, I couldn't solve the problem. Do I have to include something equivalent to the header-files in C programming language?

My second question ist the following:
I want to separate my classes from the program. Is there any possibility to generate something like object-files containing my classes?

I hope you can help me.
Thanks and best wishes!
Sebastian