email: Where does the datetime stamp in the From_ line of an mbox mail message stem from?

I am currently working on a program converting mailbox files from an old, tenex based mail format to mbox. The tenex mailbox format has separator lines like the mbox format (the latter is called the From_ line), tenex: 7-Feb-86 21:41:21-EST,1925;000000000000 mbox: From mail@example.com Fri Feb 07 14:20:00 1986 but due to a lack of documentation, the origin of the datetime stamp in the separator line of a "tenex formatted" file is obscure. Hence, when transforming a message from the tenex to mbox format, I used the datetime stamp from date-header field for constructing the From_ line for the mbox formatted message, not the one in the separator line of the tenex formatted file. But RFC4155 , an attempt to describe "the" mbox format (there are actually several different formats) and supply a kind of standard for this file format, states: > Each message begins with a separator line that identifies the message > sender, and also identifies the date and time at which the message was > received by the final recipient (either the last-hop system in the > transfer path, or the system which serves as the recipient's > mailstore). Hence, I am in doubt that my approach using the datetime stamp from the date header field is correct. But, without having the transport envelope, from where can I get the actual datetime stamp of the final recipient receiving the message? Is this the datetime stamp in the last entry of the of Received header field(s)?