use encryption tls:
Port 587:
This is the default mail submission port. When an email client or server is submitting an email to be routed by a proper mail server, it should always use SMTP port 587.
This port, coupled with TLS encryption, will ensure that email is submitted securely and following the guidelines set out by the IETF.
All Mailgun customers should consider using port 587 as default SMTP port unless you’re explicitly blocked by your upstream network or hosting provider.
