>>> "AS" == Andreas Schwab <schwab@linux-m68k.org> writes:

> On Feb 10 2019, Adam Sjøgren <asjo@koldfront.dk> wrote:
>> To: undisclosed-recipients:;

> This is the RFC2822 group of mailboxes, with the list of mailboxes being
> empty.

>    When it is desirable to treat several mailboxes as a single unit
>    (i.e., in a distribution list), the group construct can be used.  The
>    group construct allows the sender to indicate a named group of
>    recipients. This is done by giving a display name for the group,
>    followed by a colon, followed by a comma separated list of any number
>    of mailboxes (including zero and one), and ending with a semicolon.
>    Because the list of mailboxes can be empty, using the group construct
>    is also a simple way to communicate to recipients that the message
>    was sent to one or more named sets of recipients, without actually
>    providing the individual mailbox address for each of those
>    recipients.

Thanks but any idea how gnus could be configured to show that behavior
of inserting undisclosed recipient into the To field?

Bcc: testname:user1,user2;

Did not put in undisclosed recipient.