Enable to send ad-hoc custom email to a list
Please add a feature to send a one-time ad-hoc custom email to an existing list.
This is very useful for special needs, to send a special message to a list, say, like verifying their will to be subscribers and other tasks.
This also use the MP selected sending system (MP, SES or Sendgrid).
The Wordpress subscribe2 plugin has this ability, see the attached screenshot.