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A properly configured mail server needs: Port 25 (SMTP), 587 (Submission with STARTTLS), 465 (SMTPS), 993 (IMAPS), 995 (POP3S), and 443 for webmail.
Many ISPs and cloud providers block outbound port 25 to prevent spam. If it's blocked on your server, contact your hosting provider.
Port 587 uses STARTTLS (starts unencrypted then upgrades to TLS). Port 465 uses implicit TLS (encrypted from the start).