Adding Migadu email to AWS S3 static site with NameCheap domain

I'm trying to add domain email (via Migadu) to my static site that's hosted on AWS S3 through Route 53. I bought the domain name on NameCheap. I've copied the MX et al. records from Migadu into Route 53 but Migadu still gives me a DNS error, saying that it can't find the MX records for that domain. Does anyone know why this might be? Do I need to do something on NameCheap as well as or instead of Route 53? I appreciate any ideas ... I've been working on this for several days and can't imagine what I'm doing wrong.