it is very well described in the distribution-list-settings-dialog - and in the help:
To field (suppressing the list of recipients): Entering an address in this field will force Pegasus Mail to suppress the listing of all the recipients' addresseses in the To: field when you use the list. Instead of showing every member of the list, the To: field will contain only what you enter here. Because of the way Internet mail works, you cannot simply enter any piece of text in this field -- you must enter something which can be legally processed as if it were an address. We recommend that you use the following format to create the contents of this field:
"(descriptive text)" <(your own address)>
Replace (descriptive text) with a meaningful name for the mailing list, and put your own address where it says (your own address). Recipients will almost always see the descriptive text instead of your address so it will not seem as strange as it sounds. The quote characters around (descriptive text) and the angle bracket characters around (your own address) are vitally important and must be included exactly as shown. It is not possible to suppress the recipient list for MHS mail and this field will be ignored for MHS messages.
<P>it is very well described in the distribution-list-settings-dialog - and in the help:</P>
<P>To field (suppressing the list of recipients): Entering an address in this field will force Pegasus Mail to suppress the listing of all the recipients' addresseses in the To: field when you use the list. Instead of showing every member of the list, the To: field will contain only what you enter here. Because of the way Internet mail works, you cannot simply enter any piece of text in this field -- you must enter something which can be legally processed as if it were an address. We recommend that you use the following format to create the contents of this field:</P>
<P>"(descriptive text)" &lt;(your own address)&gt;</P>
<P>Replace (descriptive text) with a meaningful name for the mailing list, and put your own address where it says (your own address). Recipients will almost always see the descriptive text instead of your address so it will not seem as strange as it sounds. The quote characters around (descriptive text) and the angle bracket characters around (your own address) are vitally important and must be included exactly as shown. It is not possible to suppress the recipient list for MHS mail and this field will be ignored for MHS messages.</P>