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Re: Submission and SMTP SRV records

2004-03-16 16:27:20

On 3/16/04 at 4:22 PM -0600, Eric A. Hall wrote:


Cool. Always good to read documents; I have to pay more attention. :-) In there, you write:

        b.  Extract the mail domain element from the user's email
            address, and append the "_submission" and "_tcp" labels to
            the left of that domain name.

Have any of the big ISPs deployed the appropriate records to try this yet?

On 3/16/04 at 5:33 PM -0500, Keith Moore wrote:

Is anyone implementing SRV records for either SMTP or for Submission (i.e., SMTP SUBMIT extension)? Some talk about implementation raised some questions:

I hope that nobody is doing this in shipping product.

Not that I know of. This was talk about what could (and should) be desirable as a future feature.

For instance even if there were SRV records pointing to an SMTP server, existing clients would not recognize them - they would be looking for MX or A (or perhaps AAAA) records. And new SRV-aware clients would behave differently than existing clients, leading to more difficulty in tracking down problems.

I was actually more interested in whether anyone was doing something like this internally for relaying between internal machines that used alternate ports for only that purpose. I didn't really imagine that this would be a good thing to transition to in order to replace MX in the bigger picture.

- SRV for submission is an interesting way for an client to figure out which server/port it should contact, but what exactly would the query look like?

SRV for submission is slightly more interesting. I don't see the harm in using SRV as part of an MUA configuration mechanism as long as it's always possible for the user to override the settings. For a variety of reasons it's not always reasonable to use a submission server associated with a From address, but it might be a useful way to supply defaults.

That's what I was looking for.

(It's _much_ less reasonable to base the query on the source IP address. The last thing we need is more location-specific variation in network behavior.)

I thought you'd like that suggestion, Keith. ;-)

Offhand, it seems like just solving the configuration problem for mail submission is too much work for too little gain.

It seems to me if (e.g.) Hotmail (or even a large corporate network) could deploy an SRV for their submission servers (round-robin'ed or weighted appropriately) and clients supported the SRV, that would be a lot of bang for the buck in simplifying the most straightforward user configuration.

What you'd really like to do is solve the entire MUA configuration problem.

That's what ACAP was supposed to do, but it hasn't gotten much traction, I think at least in part because it tried to solve the whole problem.

SRV might be part of the picture, but trying to do all of this with SRV seems like a tall order.

I think it might address this particular config problem (and perhaps POP/IMAP server) quite well.

Pete Resnick <>
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