Arnt Gulbrandsen
About meAbout this blog
2017-03-01

Using procmail as an autoresponder

Procmail is old and almost forgotten, but still works well. This short script is the autoresponder for jøran@blåbærsyltetøy.gulbrandsen.priv.no:

:0 c
/tmp/jøranmail

:0
* !^FROM_DAEMON
* !^X-Loop:
* !^Auto-Submitted:
| (formail -r -t -I"From: Jøran Øygårdvær " -A"Auto-Submitted: auto-replied" -A"Mime-Version: 1.0" -A"Content-Type: text/plain; charset=utf8" -A"Content-Transfer-Encoding: 8bit" ; echo "Liker du blåbærsyltetøy? Jeg synes blåbærsyltetøy er veldig godt." ; echo ; echo "-- " ; echo "Jøran") | /usr/sbin/sendmail -t

The first clause stores all incoming mail in /tmp/jøranmail just in case it's needed for debugging. The second clause filters out three kinds of mail that should not receive an autoreply. For messages that pass all three hurdles, it runs formail with many arguments to create an EAI-compliant autoreply header, echo to write a brief reply, and sends the result back.

It may not be terribly readable, but it's brief and reliable. That glass is two thirds full, not one third empty.

2017-01-20

A new email address

I think mail to आर्न्ट@यूनिवर्सल.भारत should now land in my inbox... wonder how long it'll take before the first spammer manages to spam that address.

2017-01-19

Three programs, one feature

It's not something one does often, but I've implemented the same feature in three different programs. Not very different, all are written in the same programming language for the same platform, and all are servers.

Same platform, same language, same task, same developer... you would think the three patches would end up looking similar? They did not, not at all.

The feature I wrote is is support for using UTF8 on SMTP, which I've implemented for Postfix, Sendmail and Qmail, which all run on linux/posix systems. I tried to follow the code style for each of them, and surprised myself at how different my code looked.

One patch is well-engineered, prim and proper.

The next is for an amorphous blob of software. The patch is itself amorphous, and makes functions even longer that were too long already. Yet it's half as long as the first patch. The two are, in my own judgment, about equally readable. One wins on length, the other on readability, they're roughly tied overall. This surprised me not a little.

The third is a short, readable patch which one might call an inspired hack. It's a much smaller than the others and easily wins on readability too.

It wasn't supposed to be like that, was it? Good engineering shouldn't give the most verbose patch, and the hack shouldn't be the most lucid of the three.

I see two things here:

First: Proper engineering has its value, but perhaps not as much as common wisdom says. Moderately clean code offers almost all of the value of really clean code.

Second: A small program is easy to work with, such as the MVPs that are so fashionable these days. But ease of modification isn't all, the smallest among the three servers has fallen out of use because the world changed and it stopped being viable.

Some random verbiage on each of the three servers and patches: (more…)

2017-01-07

Use UTF8 or Punycode for email addresses?

Unicode addresses in email, such as مثال@مثال.السعودية, can be written using either Punycode or UTF8. (Or, if you're feeling inventive, in another manner you invent.) Which is best?

UTF8 looks like this: From: Arabic Example <مثال@مثال.السعودية>, punycode is From: Arabic Example <xn--mgbh0fb@xn--mgbh0fb.xn--mgberp4a5d4ar>.

The answer follows from two of the design goals for the unicode email extensions:

  1. Allow UTF8 everywhere
  2. Extend email, don't restrict it

RFC 821 and its successors do not contain any rules such as you MUST NOT put the letter n next to an x, so Punycode is allowed. EAI allows Punycode by virtue of not forbidding what was previously allowed. But the right way is to use UTF8 everywhere. Use UTF8 in the subject field, in the body text, in the address… everywhere! That's allowed, it's a design goal, and it's better than Punycode for four reasons.

First, it's simpler than using Punycode in addresses, 2047 encoding in the subject text and qp/b64 encoding in the body text.

Second, it's very, very readable. A surprising amount of legacy software does the right thing if you send it UTF8, and that goes for humans who read email source too.

Third, Punycode is specified for the domain part of addresses, but not for the localpart, and if rumour is to be believed, people are using two incompatible encodings for the localpart. (In the example above, the second and third instances of xn-- are specified, but the first is not and one vendor reputedly does it differently.)

Fourth, sending Punycode habituates users to accept random hex blobs in addresses. A phisher's dream.

So use UTF8 everywhere in the message. Mapping to Punycode is necessary when doing the MX lookup in order to transmit the message, but only then.

2014-07-22

Installing and testing Postfix with unicode address support

By request: A step-to-step guide to installing/testing unicode addresses with Postfix. Perhaps overly detailed.

I'll use a new linux/ubuntu host here. As it happens, I use a 64-bit ubuntu 14.04 at Amazon.

The following commands prepare the host. This updates the host with the latest package database and packages, so that the later commands won't fail due to package inavailability or version conflicts. (more…)

2014-06-12

Implementation notes about unicode mail

I've implemented unicode mail three times now; in Postfix (paid for by CNNIC and not yet integrated), in aox and lastly in an old mail reader I'm porting from the Zaurus PDA to Android (unreleased as yet, send me mail if you'd like beta access). This is mostly a random collection of notes and remarks I collected while writing the code.

The specification was produced by an IETF working group called EAI (short for email address internationalisation). The WG produced two generations of RFCs. First, an experimental series which I ignore, then a revised, simplified and improved series. This covers the second generation, which takes the general position that unicode mail is only sent to recipients who understand it. There is no conversion during transport, and (almost) no fallback to ASCII.

RFC 6530 is an overview/introduction. It points to the other documents, and has some extra text. Worth reading.

6531 describes how unicode addresses are used with SMTP: MAIL FROM, RCPT TO and VRFY accept UTF8 addresses, and there's a safeguard to provoke a syntax error in case a unicode message body would otherwise reach someone who cannot accept it. (more…)

2014-05-09

A unicode email autoresponder

I've set up a test address for the SMTPUTF8 extension created by the IETF EAI working group.

If you send mail to jøran@blåbærsyltetøy.gulbrandsen.priv.no Jøran will send you a stock reply, which you can use to test that unicode mail works in both directions.

For the moment you must be able to send via IPv6. Jøran can send the reply back via either IPv4 or IPv6, but you have to send the initial message via IPv6. I intend to add a v4-capable secondary MX later.

I have or can arrange other testing too; send me mail if you're interested.

2013-07-28

Test messages for unicode mail addresses (EAI)

EAI is a set of RFCs to enable unicode email addresses. jøran@example.com and even jøran@blåbærsyltetøy.no are syntactically valid email addresses. There are RFCs to extend the email message syntax, to transmit these messages via SMTP, access them via POP and IMAP, and to provide read access by unextended IMAP/POP clients.

I wrote a set of test messages for EAI this morning and put them on github. Feel free to send me extensions and corrections.