Is TLS opportunistic or enforced on your mail gateway?
By default, Alloy is designed to opportunistically try outbound TLS v1.2 or higher when attempting to deliver email. This means that if your recipient’s email server accepts an inbound TLS v1.2 or higher connection, Alloy will deliver the email over a TLS encrypted connection. If the server does not support TLS, Alloy will deliver the message over the default unencrypted connection.