mh-auto-fields-list

mh-auto-fields-list is a variable defined in `mh-e.el'.
Its value is

nil

Documentation:
List of recipients for which header lines are automatically inserted.

This option can be used to set the identity depending on the
recipient. To customize this option, click on the "INS" button and
enter a regular expression for the recipient's address. Click on the
"INS" button with the "Add at least one item below" label. Then choose
one of the items in the "Value Menu".

The "Identity" menu item is used to select an identity from those
configured in `mh-identity-list'. All of the information for that
identity will be added if the recipient matches. The "Fcc Field" menu
item is used to select a folder that is used in the "Fcc:" header.
When you send the message, MH will put a copy of your message in this
folder. The "Mail-Followup-To Field" menu item is used to insert an
"Mail-Followup-To:" header field with the recipients you provide. If
the recipient's mail user agent supports this header field (as nmh
does), then their replies will go to the addresses listed. This is
useful if their replies go both to the list and to you and you don't
have a mechanism to suppress duplicates. If you reply to someone not
on the list, you must either remove the "Mail-Followup-To:" field, or
ensure the recipient is also listed there so that he receives replies
to your reply. Other header fields may be added using the "Other
Field" menu item.

These fields can only be added after the recipient is known. Once the
header contains one or more recipients, run the
M-x mh-insert-auto-fields command or choose the "Identity -> Insert
Auto Fields" menu item to insert these fields manually. However, you
can just send the message and the fields will be added automatically.
You are given a chance to see these fields and to confirm them before
the message is actually sent. You can do away with this confirmation
by turning off the option `mh-auto-fields-prompt-flag'.

You should avoid using the same header field in `mh-auto-fields-list'
and `mh-identity-list' definitions that may apply to the same message
as the result is undefined.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 7.3 of the MH-E package that is part of Emacs 22.1.