What I ended up doing is adding a DNS zone for infantex.com.mx (althoug it won't be used), deactivating DKIM for the domain and activating it again so that a DKIM record was created, and copied it's contents to Cloudflare. It seems to have worked. I used mailgenius to check it. DKIM turned out to be OK, but I was surprised to learn that both my domain (infantex.com.mx) and the VPS's IP (65.19.141.197) were blacklisted! Mailgenius report: https://app.mailgenius.com/spam-test/979562 Howe