It's not clear exactly what the problem is here. ".eml format" is not entirely well-defined, but what you'll find inside those files is certainly honest-to-Postel RFC5322 (née 822) standard email format.
Procmail supports a few folder formats but what differs between them is mainly how the files are organized.
- Berkeley mbox format is a single file with a
From_ line prepended before each individual message. This is the traditional standard format for local mailboxes. It is the default format for Procmail delivery if the destination is not a directory.
- MSGPREFIX format is one file per message, like what you are experiencing now. The message prefix can be configured, but there is no built-in way to add an
.eml file extension, if that's what you're asking.
- MH format is vaguely similar, only the file names are simply numbers.
- Maildir format is the modern standard for many mail servers; it is a directory with subdirectories named
new, tmp, and cur. Within those directories, each file name is a long unique identifier which is assigned based on a number of factors to ensure that it is unique and safe.
Anything else, you need to write an explicit rule, or call an external utility. (For example, some IMAP servers want you to always call their delivery utility, which takes care of also adding the message to the server's indices, etc.)
Which directory-based format is selected depends on how the directory name is formatted in the rule (dir vs dir/ vs dir/.), and IIRC some heuristics to determine whether the Maildir subdirectories already exist.
See also https://www.iki.fi/era/procmail/mini-faq#appendix-folders
By the way, to unconditionally execute a recipe, just leave out the condition line entirely. To simply deliver all mail to a single location, it suffices to set DEFAULT to that folder path.
