Hi,
"Mail to custom field" is a new plugin which has been added just before the previous release ; it for a customer request.
With the rush I forgot to write the documentation (and because I'm still in the rush for the HikaMarket release, I still have documentation pages in my TODO list)
The plugin allow you to send an email to an address specify in a custom field (order custom field or item custom field).
The mail send will be the "hikaserial - mailtocustomfield" one.
The plugin will also call the "attach serial" plugin, to attach the serial image if there is one.
So you can create an order/item custom field and let your customer enter an email address to send the special mail (that you can override in the HikaShop email backend) to the targeted email.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.