This is currently happening to my email domain. Gets rejected as it doesn't have a valid hash (recipient name), but the logfiles are full of <3 letters>@mydomain.com and <english_word>@mydomain.com rejections.
Yeah, this is an age-old issue -- in the early 00s, my mom got a domain and used the email <first_initial>@<domain>.com. She gave up battling the deluge of spam after about a year. We looked through the logs, and saw that her next choice of handle was also getting tons of spam, too, because it was also short.