Let's see whether email submission works.

So what did the email you sent look like?

To: report@bugs.python.org
Subject: Test issue [assignee=gvanrossum]

The body was msg63609.

The tricky part is to get the property names right. Roundup will reject 
(and return) the message if they are wrong, without telling what the 
right ones are. For issue, we currently have

title
(messagea)
(files)
nosy (*)
superseder
type
components (*)
versions (*)
priority
dependencies (*)
assignee 
status
resolution
keywords (*)

The ones in parentheses are irrelevant for the subject. The ones with an 
asterisk are multilink, so you can not only key=value, but also 
key=+value or key=-value (see the body of the email here for syntax 
examples)

So what's the syntax for setting multiple attributes via an email subject?
[assignee=+twouters,priority=low]?

Picky!

[assignee=guido]

Does it also work in the body of the message?

No.

Guido van Rossum schrieb:
> Guido van Rossum <guido@python.org> added the comment:
> 
> So what's the syntax for setting multiple attributes via an email subject?
> [assignee=+twouters,priority=low]?

assignee is not multilink, and the separator is semicolon (;); 
otherwise, that's the syntax. , is the separator multilink values.
[nosy=richard,cliff]