I know from experience I've had a good number of emails go to my "spam" folder even though they are not spam.
Some commissioners also get A LOT of emails and honestly don't have time to respond to every one of them. From my own experience, there have been times where I would spend 3-5 hours JUST doing email (send quotes, regrets, updates...) and it's on top of a full time job, commission sewing, my own sewing, family/life, and school. Every day was at least 1 hour of emails and then the 3-5 would be on, let's say, a Sunday night.
It's really hard to keep up on. Once you fall behind, it's a constant catch-up that never ends. It's just one person, doing everything, from work to customer service. Sometimes, you just gotta let some slide and unfortunately not respond.