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Re: draft-daboo-srv-email

2010-01-08 13:17:28

Russ Allbery wrote:

Hector Santos <hsantos(_at_)santronics(_dot_)com> writes:

2) What about outgoing?

Are MX records considered the solution?

Using GMAIL as an example, I think it only allows IMAP for receiving and
SUBMIT (port 587) for sending.  So wouldn't a SRV record be useful for
the case where SMTP is used for outgoing when the incoming uses IMAP?

As a site where, for various load-balancing, administrative, and
configuration complexity reasons, our outgoing mail servers for clients
are entirely distinct from the inbound servers holding the MX records of
the domain, I would love to see a SRV record for clients to locate
outbound SMTP servers.

I missed section 3.1 which offers the _submission._tcp.domain SRV query.

Don't know if that covers, partially or otherwise, the user needs on your end.

The only thing I see is that normally, the posting host can either be specific (i.e, "smart host") or MX lookup. But I think it is MUA specific too.

A quick review of how TBIRD does it for "Create New Account", it will use the "default" smtp server setup prepared for the account settings. So the outgoing part is probably best useful when the user is first installing his/her MUA.

Also, in terms of a "USER" need, the odds are good his ISP is blocking port 25 for anything other than the ISP email network. So for non ISP networks, port 587 "SHOULD" be a preferred selection if offered by the mail host.

In my experience, and I helped the TBIRD guys get this added, this is more important in the growing SOHO or wireless home network with additional user machines are used.

For SMTP receivers who are "strict" with the EHLO domain literal IP checking, this can be a problem when the MUA uses the user machine IP and not the NAT or public IP address for the user.

OE does not have this problem because it will use the netbios computer name. TBIRD will use a bracket IP of the user' machine.

So I had the TBIRD people address this and the final simple/quick solution was an Advanced Configuration option (rather than add a new DIALOG) that allows the EHLO string to be defined.

      Tools | General | Config Editor

Type the filter


to see all the mail server fields. I don't recall if I had to add te first time (in the first beta) and its now added automatically, but there would be fields called


and if defined, it will be used as the override for the SMTP going transaction EHLO command. Otherwise, it will use the FQDN for a public address or the private ip address of the user's machine.

For example from my SOHO machine I have my TBIRD mail.server.server#.hostname fields set using

         [public IP address]

Finally, before this feature was added to TBIRD, because I was using a SUBMIT server it may have a tight EHLO checking. I proposed to Klensin and Gellens (RFC 4409) that they consider adding some notes for relaxing EHLO IP literal checking because SUBMIT requires authentication anyway which is handled after the EHLO state.

So for our WCSMTP software, we added an option (enabled by default) to skip EHLO checking for PORT 587 connections based on the idea that authentication is required anyway, not an option like in public port 25. That was our solution before the TBIRD changes were made.


Hector Santos

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