Our underlying SMTP vendor, Sparkpost, has reported an intermittent issue with email deliverability that might caused some delays in dispatching mails via Sitecore EXM and Email Cloud solutions.
More details: https://status.sparkpost.com/incidents/fblwmlc5x9kk
Resolved: The issue was active during 1:30 PM - 4:30 PM UTC and now mitigated. No further impact expected.