Right now the sending of 'nosy' messages is handled by
IssueClass.nosymessage. This messages determines whom to send a given
message to, based on the issue's 'nosy' property.

Users may want to modify the way this message is sent out. For example,
they may want to send multiple mails, where addresses are grouped by
certain criteria (to hide customers from each other, say).

Is there any reason this code could not be moved into the nosyreaction
class itself (or a baseclass, if it is used elsewhere, too) ? That would
allow it to be customized.