Today, SMAX does not support Emojis, they have to be manually deleted if you have to copy - paste from E-mail.
But, if you use OPB e-mail integration they are simply refused, but still the mail is put in the processed queue. This will be fixed in SMAX 2020.08 patch 2, when the customer will receive an error message. this will probably mean that the customer will call the helpdesk, which is not what we want to happen. This is actually quite a big problems as more and more end users put emojis in their automatic greeting, which means they are unable to add a case to SMAX via E-mail.
The best thing would be is SMAX could support emojis however it is received.