Quiet “short” point of view, aside being wrong (sending a mail, being “so much faster”, really? That’s a router, not a SMTP relay).
FQDN should be possible, not only IP. But I guess that’s not a high priority change in routerOS, compared to CIFS features and fixes. “lol”.
Btw, I use as a workaround for this issue a simple script to be scheduled according to your needs.