Thank you for your response.
I copied the DKIM exactly as indicated in the DreamHost panel (and entered it in the Cloudflare DNS settings):
“v=DMARC1; p=quarantine; fo=1; rua=mailto:0ebf045ffd7547dc8e2d634c62fd2a6b@dmarc-reports.cloudflare.net,mailto:dmarc_agg@frontnieuws.com; ruf=mailto:dmarc_forensic@frontnieuws.com; pct=100”
Previously, there was no problem, but for the past 4 days, about a third of the newsletters have been bouncing back.