Opportunistic:
Communicates using encryption if the peer supports and elects to use TLS
Communicates without encryption if the peer does not support TLS
Communicates without encryption if the peer supports TLS but elects not to use TLS
Mandatory:
Communicates using encryption if the peer supports and elects to use TLS
Does not communicate if the peer does not support TLS
Does not communicate if the peer supports TLS but elects not to use TLS
To ensure messages can be received from the Hosted Email Security MTA, configure your firewall to accept email messages from the following Hosted Email Security IP address / CIDR blocks:
Europe, the Middle East, Africa
52.48.127.192/26
52.58.62.192/26
52.58.63.0/25
All other regions
54.219.191.0/25
54.219.188.0/26
54.86.63.64/26