Hope this helps...

http://www.lsoft.com/manuals/1.8d/owner/owner.html#5.3.1

5. Setting Subscription Options For Subscribers
5.3. Options that may be set
5.3.1. Mail/NOMail

Setting this option to Mail indicates that the subscriber will receive
mail from the list. NOMail is the complementary command that
stops mail but leaves the user subscribed to the list. (NOMail is often
a good compromise for users who are leaving the office for vacation
or on extended business trips, and who don't want a full mailbox on
their return.) The format of the messages received is controlled by
the DIGEST/INDEX/NODIGEST/NOINDEX options (see below).



5.3.2. DIGest/NODIGest

Causes the subscriber to receive one posting per digest cycle (typically
daily) rather than individual messages as they are processed by
LISTSERV.

In version 1.8b and later, the MAIL/NOMAIL option has been isolated from
DIGEST/INDEX. The MAIL/NOMAIL option controls
whether messages should be delivered, and the
DIGEST/INDEX/NODIGEST/NOINDEX option controls the format in which
messages
should be delivered. Thus, switching to NOMAIL and back to MAIL now
preserves the digest/index/normal delivery setting. To provide as
much compatibility with the old syntax as possible, the four options
operate as follows:

DIGEST: enable digest delivery mode (which negates INDEX), enable mail
delivery. No change from version 1.8a.

INDEX: enable index delivery mode (which negates DIGEST), enable mail
delivery. No change from version 1.8a.

NOMAIL: disable mail delivery. No change from version 1.8a.

MAIL: restore mail delivery, without altering the digest/index/normal
delivery setting (new behavior). For compatibility with 1.8a, if mail
delivery was already active, the MAIL option negates INDEX/DIGEST. Thus,
a user going from NOMAIL to MAIL will keep his previous
delivery options, whereas a user going from DIGEST or INDEX to MAIL will
in fact deactivate index/digest mode.

To revert from digest/index subscription mode to normal delivery, you
can use either the MAIL option as before, or the
NODIGEST/NOINDEX option. The NODIGEST and NOINDEX options were actually
present in versions 1.7f and 1.8a, as synonyms for
the MAIL option. In other words, you can update your instructions to
indicate that the DIGEST/INDEX options are negated by the
NODIGEST/NOINDEX options, even if you are still running an older version
of the software.

Note that in extreme cases, subscribers using the DIGEST option may
receive more than one digest per cycle if the digest limit is reached
before the end of the cycle.