The "Bcc:" field (where the "Bcc" means "Blind Carbon Copy") contains addresses of recipients of the message whose addresses are not to be revealed to other recipients of the message. There are three ways in which the "Bcc:" field is used. In the first case, when a message containing a "Bcc:" field is prepared to be sent, the "Bcc:" line is removed even though all of the recipients (including those specified in the "Bcc:" field) are sent a copy of the message. In the second case, recipients specified in the "To:" and "Cc:" lines each are sent a copy of the message with the "Bcc:" line removed as above, but the recipients on the "Bcc:" line get a separate copy of the message containing a "Bcc:" line. (When there are multiple recipient addresses in the "Bcc:" field, some implementations actually send a separate copy of the message to each recipient with a "Bcc:" containing only the address of that particular recipient.) Finally, since a "Bcc:" field may contain no addresses, a "Bcc:" field can be sent without any addresses indicating to the recipients that blind copies were sent to someone. Which method to use with "Bcc:" fields is implementation dependent, but refer to the "Security Considerations" section of this document for a discussion of each.
This function will go to the next line of non-quoted text which comes after a line of quoted text in the internal pager.
以及用於切換引文是否顯示的：
1 2 3 4 5 6 7
<toggle-quoted> (default: T)
The pager uses the $quote_regexp variable to detect quoted text when displaying the body of the message. This function toggles the display of the quoted material in the message. It is particularly useful when being interested in just the response and there is a large amount of quoted text in the way.
Reply-To
這個郵件首部爲用戶回覆郵件時提供建議，設定新郵件的To:首部。
Thread
References
In-Reply-To
format=flowed
Mail-Followup-To
回覆郵件時如果選擇了follow up(或者說reply to
all)的方式，那麼收件人會被填爲Mail-Followup-To設定的地址。
避免發件人如果訂閱了該郵件列表的話收到兩封相同的郵件。