[Mailman-Users] Is Character Permitted

[Bill Cole]

Mailman Admin wrote, On 11/9/11 10:25 AM:
> On 2011-11-09 09:55, David Andrews wrote:
>> Is the "&" character allowed in a list name, such as in:  "art&artists?"
>
> No, as it must be a valid email address.
> In email addresses are only the following characters allowed
> a to z
> A to Z
> 0 to 9
> .
> -
> _


That is quite significantly incorrect.

Refer to RFC5322 section 3.2.3 (http://tools.ietf.org/html/rfc5322#page-13) 
which defines the syntax of the "atom" and its sub-unit "atext" which are 
the building blocks for the local part of an email address. The allowed 
characters (the "atext" set) in the "atom" components of an address 
local-part (delimited by '.') which do not use the unusual quoted string 
syntax are all printable ASCII except for whitespace and these 13 characters:

<>[]()@;:.\,"

That character set has been unchanged in the Internet Message Format RFC's 
going back to RFC822. Obviously, the '.' is barred from the "atom" 
components of a local-part because it is used between them. See RFC5322 for 
the full ABNF spec. RFC5321 (the SMTP specification) refers to the RFC5322 
spec.

Whether *Mailman* handles '&' correctly in a list name is a different 
question. There are many cases of mail software being more restrictive than 
the specification about addresses, and I have not dug into the Mailman docs 
to nail down what it will accept as a list name. Also, I would be very 
uneasy about using any character (like '&') which is commonly used with 
special meaning in languages that are popular on Unix systems. I know that 
Python is generally pretty good about strings containing metacharacters, but 
when you send mail you never know what else other than your own tools will 
have to handle it. In a world full of perl, shell, m4, and sendmail.cfese I 
would be very dubious about using addresses containing ampersands, 
backticks, apostrophes, and other theoretically acceptable characters. They 
are formally legal but if you are picking an address to use, you should 
avoid making making such challenges to code quality.