webmailer that can send emails delayed/scheduled

Hi,

I run Horde and Afterlogic as webmailers.
Both cannot schedule when an email is sent.

Does anyone know a webmailer or PHP-program that can do this?
Preferably small and easy.
Or is writing my own PHP-Program the only solution?

I do not want to use PHPLists for it because that is overkill.

Regards,
Jan