Hi,
Thanks for your feedback.
Unfortunately, this won't be possible.
HikaShop has no email queue system, which means that if we were to implement that capability, we would have to send all the selected emails at once. However, hosting servers usually block the sending of too many emails at once, in order to reduce spam.
That's why email extensions like AcyMailing have a queue system to spread the sending of the emails over time as to not get flagged.
Moreover, email servers usually have an internal queue to process the emails. So normally, if there is a problem on the server, the emails are still queued on the email server and they can be sent by the email server when it gets back online. So most of the times, resending a lot of emails shouldn't be necessary.