What is opportunistic TLS encryption?

Opportunistic TLS (Transport Layer Security) refers to extensions in plain text communication protocols, which offer a way to upgrade a plain text connection to an encrypted (TLS or SSL) connection instead of using a separate port for encrypted communication.

Does Exchange 2010 use TLS by default?

Exchange 2010 can use TLS 1.2, but it is disabled by default. This means that it will continue to work with TLS 1.0 and TLS 1.1, but the preferred way of communicating is TLS 1.2. If Microsoft will contact your Exchange server using TLS 1.2 and you’re server does not accept this you might run into communication issues.

How do I enable opportunistic TLS?

Enable Outbound TLS

1. Open Internet Information Service (IIS) 6.0 Manager ;
2. Select a SMTP Virtual Server -> Right Click -> Properties -> Delivery -> Outbound Security -> Check TLS encryption -> Click OK -> Click Apply .

Does Exchange Online use opportunistic TLS?

By default, Exchange Online always uses opportunistic TLS. Unless you have configured Exchange Online to ensure that messages to that recipient are only sent through secure connections, then by default the message will be sent unencrypted if the recipient organization doesn’t support TLS encryption.

What does Opportunistic TLS mean in Exchange Server?

This is the parameter that “activate” the option of opportunistic TLS The meaning is that, in a scenario in which other mail server try to communicate with the Exchange server, the Exchange server will offer to use TLS. If the “other mail server” doesn’t support TLS, the Exchange server will “agree” to use the SMTP protocol instead.

What happens if Exchange Online does not support TLS?

If the receiving server does not support TLS 1.2, Exchange Online being opportunistic will try to send email without TLS. If the receiving mail server does not have TLS enforced for inbound email flow, the email will be sent without TLS.

How to force TLS on exchange on-premises environment?

To be able to fulfil the requirement, in which each E-mail message sent by Exchange on-Premises to the external mail server (Exchange Online in our scenario), that represent the domain name – o365pilot.com will be encrypted, we will create a new Send mail connector

When to use TLS for client to server?

The option of – Offer Basic Authentication only after starting TLS is relevant to “client to server” scenario, in which mail client that uses POP3/IMAP4 need to connect the Exchange on-Premises server by using TLS protocol.