Mboxed

… library plus tools for mbox files, written in the Go programming language.

This is free and unencumbered software released into the public domain.

mboxmux

The mboxmux(1) tool can split mailboxes based on header values. Run go install github.com/pascaldekloe/mboxed/cmd/mboxmux@latest for a local build.

Usage of mboxmux:
  -d directory
    	Set the directory for output files. (default ".")
  -default file-name
    	Sets a default output file-name for messages that would have been omitted otherwise, which are no name, . and .. specifically.
  -escape replacement
    	Sets the replacement for '/' occurences in output files. (default "_")
  -header name
    	Define the header (name) used for file distribution.
  -tokentrim pattern
    	Add a pattern for token omission on the output files. The first character in the pattern defines the token separator, and the remainder sets the token to be excluded. E.g., -tokentrim ,Opened omits any Opened occurences in a comma-separated list, i.e., Inbox,Opened,Important would become Inbox,Important. Multiple tokentrim arguments are applied in conjuntion.

The following command splits a “takeout” from GMail into separate mailboxes.

mboxmux -d mailboxes -header X-Gmail-Labels -default Misc \
	-tokentrim ',Opened' -tokentrim ',Unread' \
	-tokentrim ',Archived' \
	-tokentrim ',Category Personal' \
	-tokentrim ',Category Promotions' \
	-tokentrim ',Category Purchases' \
	-tokentrim ',Category Social' \
	-tokentrim ',Category Travel' \
	-tokentrim ',Category Updates' \
	-tokentrim ',IMAP_Forwarded' -tokentrim ',IMAP_$Forwarded' \
	-tokentrim ',IMAP_Redirected' \
	-tokentrim ',IMAP_NotJunk' -tokentrim ',IMAP_$NotJunk' \
	-tokentrim ',IMAP_Junk' -tokentrim ',IMAP_$Junk' \
	-tokentrim ',IMAP_JunkRecorded' \
	-tokentrim ',IMAP_$MailFlagBit0' \
	-tokentrim ',IMAP_$MailFlagBit1' \
	-tokentrim ',IMAP_$MailFlagBit2' \
	bu1.mbox bu2.mbox bu3.mbox