Documentation bug: https://github.com/asterisk/asterisk/blob/master/configs/samples/voicemail.conf.sample#L350
attachextrecs is a misnomer. This option actually controls whether an email is sent at all when a recording is added to a mailbox using MixMonitor. It doesn't have anything to do with whether the recording is attached or not. That is controlled by the regular "attach" setting.
You must be