How to respond to an ex’s email

My ex broke up with me almost a year ago. We had a great relationship and amazing chemistry- but the relationship timing wasn’t right. I was devastated and blindsided by the breakup, and he started dating someone new soon after and he remains with her months later. Post-break up - I still talked to him (I initiated it) and I had to stop because it was emotionally too hard. I stopped calling months ago. He just sent me an email yesterday to give me updates on himself and asking me how I am doing. Should I just ignore him? He has been in my thoughts constantly, because I have had a much harder time moving on. But - I don’t want to cut him out completely. He is still with his GF - so why would he reach out? Should I just ignore it?