Is your ISP blocking outgoing port 25?

Frank Bulk frnkblk at
Mon Jun 22 15:52:41 UTC 2009

That’s e-mail client list covers less than 5% of my customer base and can't
be construed as a standard. =)  Even Microsoft doesn't support it in Outlook
Express or Windows Mail.


-----Original Message-----
From: Matthew Huff [mailto:mhuff at] 
Sent: Monday, June 22, 2009 10:20 AM
To: 'frnkblk at'; 'John Levine'; 'nanog at'
Subject: RE: Is your ISP blocking outgoing port 25?

It already is used by Microsoft. Do a google for +Microsoft +Autodiscover.

It is used by Outlook for Windows, Entourage for Mac, the iPhone and Windows
Mobile devices. Like you suggested, it uses DNS based on the users email
address and looks for a series of resolvable addresses the easiest being
autodiscover.domain-name.tld (it has others because of SSL cert
flexibility). It uses that address to download an XML file. 

The only tricky thing to set it up is that a lot of the documentation out
there is dated. It has changed since it was first released and a lot of the
documentation on technical blogs, and even on Microsoft's web site are
incorrect. Once it's setup, however, it's great. 

Matthew Huff       | One Manhattanville Rd
OTA Management LLC | Purchase, NY 10577  | Phone: 914-460-4039
aim: matthewbhuff  | Fax:   914-460-4139

> -----Original Message-----
> From: Frank Bulk [mailto:frnkblk at]
> Sent: Monday, June 22, 2009 11:14 AM
> To: 'John Levine'; nanog at
> Subject: RE: Is your ISP blocking outgoing port 25?
> The bootstrap question is addressed by requiring the end-user to know
> their
> e-mail address and password.  Based on the domain name, the
> implementation
> would reach out to https://something.domain-name.tld and download the
> relevant "schema" and data for IMAP, SMTP, POP3, etc, in ordered
> priority.
> Based on what the e-mail client could support, the desired settings
> would be
> displayed, and upon end-user approval, applied. This could be leveraged
> by
> RIM for their BIS, Microsoft/Gmail/etc for smartphones, and for third-
> party
> webmail hosts such as
> Frank
> -----Original Message-----
> From: John Levine [mailto:johnl at]
> Sent: Monday, June 22, 2009 9:24 AM
> To: nanog at
> Cc: frnkblk at
> Subject: Re: Is your ISP blocking outgoing port 25?
> >It's a pity that MAAWG or another group hasn't written a
> >specification for the automatic downloading of configuration (with
> >certificates, to be sure, for some kind of repudiation) and the
> >update thereof, for adoption by the leading consumer e-mail clients.
> MAAWG decided it's not in the standards business, but it does BCPs
> pointing at standards elsewhere (mostly the IETF) that it encourages
> people to follow.  Write a standard that people can use, and I don't
> think I'd have much trouble getting them to endorse it.
> It's an interesting design topic, particularly the bootstrap question
> of how the client decides where to look for its configuration.  A lot
> of this stuff is already available via DHCP, but of course a key goal
> here is to set config info the last across reboots on different
> networks.
> Followup to IETF-something, I suspect.
> R's,
> John

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