I want to enable TLS on SMTP server which installed on windows 2012 R2, however the option is grayed out. PFA (https://i.stack.imgur.com/lQ2nl.png)
I have added certificated in regedit for TLS 1.1 and TLS 1.2, however it didn't work.
Tried following steps provided here https://support.faxmaker.gfi.com/hc/en-us/articles/4717769935506-Enabling-TLS-Configuration-on-IIS-SMTP-Server
You need an SSL/TLS certificate to secure the SMTP communication. You can either obtain a certificate from a trusted Certificate Authority (CA) or generate a self-signed certificate. Then you'll have to install it on your server. Check this question on Serverfault, it's almost identical to yours and has several solutions.
Basically, here's what you have to do:
You should configure the TLS settings to enable secure communication. Open the Internet Information Services (IIS) Manager. Navigate to your SMTP server instance, right-click "Default SMTP Virtual Server," and choose "Properties." In the properties window, go to the "Access" tab, click the "Certificate..." button, and select a valid SSL/TLS certificate for your server. Next, go to the "Delivery" tab, click "Outbound Security," and select "TLS Encryption" as the authentication method. Finally, restart the SMTP service to apply the changes.