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Re: SMTP Transferred-By-Reference // Alternative to Temp Error resource protection

2007-11-16 09:46:21

On Nov 16, 2007, at 7:04 AM, John C Klensin wrote:

The user of a commercial email service that provides free mailboxes, or the user of an ISP's mail system, has _no_ practical control over the behavior of the relevant servers, despite sharing an ADMD. Yes, I control my mail servers and someone receiving mail through the servers of an enterprise for which she works could be reasonably though of as being within the same narrowly-defined ADMD, but, in the general case, no.

And, for that general case, one either

        * needs to retrieve or fetch the TBR message onto user
        equipment and then do the retrieval -- a process that
        cannot guarantee that the relevant machines are

Any transmitting MTA that is not well connected should not use the TBR extension. There are other situations where the TBR extension would not be used, such as for MUA message submission to an MSA. This extension provides an efficient alternate method to complete message transmissions that might otherwise be momentarily blocked by a receiver's Temp error. Only the MTA transmitter would need to offer a well-connected service when the benefit of the TBR extension is desired.

The TBR extension does not involve any end user interaction. An email user may benefit by having their email transmitted more expediently and with greater integrity when their provider supports the TBR extension, but there is no necessity that this extension be supported thoughout. Good things still come to those that wait. : )


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