Mpack and munpack are utilities for encoding and decoding (respectively) binary files in MIME (Multipurpose Internet Mail Extensions) format mail messages.
Mpack is a UNIX-oriented utility, and as such, it has little hope of dealing well with RMS files whose record format is anything exotic.
/ftp/mpack/mpack-1_6b_vms/vms_notes.txt
/ftp/mpack/mpack-1_6b_vms/mpack-1_6b_vms.zip
The Zip archive for the complete kit was created using the Zip "-V" option to preserve the VMS file attributes, but the source files in these Zip archives should be usable on a non-VMS system.
All versions of mpack for VMS, including older and experimental ones, may be found at the archive: /ftp/mpack/
FTP access is also available at: ftp://ftp.antinode.info/mpack/