Sorting mboxrd (efficiently)

Hello everyone,

I need to sort by date a huge mailbox (6 GB) in mboxrd format.
I tried with rmail in Emacs but it's really slow in loading and sorting
- the latter even for smaller mailboxes.

Does mailutils provide efficient sorting facilities?
I skimmed through the docs and it mentions sorting only for mh boxes.

If there's no such feature I could write it, maybe with recursive merge
sort splitting the mailbox in multiple files and then recombining them.

Let me know if this is already provided.

Many thanks and greetings,
Andrea Monaco