"rejected it" so you have answers. Sometimes recipients block or they do not agree with imposing events on their calendar.
So I had a same problem with event and I solve that in deferent way.
If I am sure of the recipient who has subscribed, for example, to the list of events, then I will send the invitation in a standard, monitored way..
If not, I send a invitation as attachment in regular email message I can monitored it but confirmation is required then.
I build COM add-in to do that: dodaj-wydarzenie
And second one to send it separately to ech address : pojedyncza-wysylka-emaili to be faster and discreet in sharing any data. That Addi-n I do not translate for else lang yet ;)
You can follow the same way.
Regards