Did you run the Setup Manager with the 'Configure' option after migrating the mailbox?  This should disperse the needed settings across the environment (such as the Connection String editor, Host Server .config file, and Environment Library).

If you've already done that, are workflows going into error state, or are they simply not sending any emails?  Are these task emails or emails from a 'Send Email' step?  Both?  Have you checked the Host Server logs during the time when an email was expected to send, but did not, and cross-checked for any error messages?

hi @chruff 

Thanks Chruff. I will do this now. I have to run Cumulative updates as well, shall I run this after the update?

Also, we have 2 prod environments, shall I run the setup manager one after another or can run simultaneously?

Please advise.

It's recommended to upgrade one node at a time, because the K2 service will go down briefly during the Configure process.  For your second question, it's always best practice to keep your K2 server on the latest CUs and fix packs, but this shouldn't be related to your email issue.

thanks @chruff 

I am receiving SourceCode.Workflow.Shapes.EWS: Autodiscover Failure: The Exchange server is not available, the password is incorrect or the e-mail address does not exist. error after update. Do you have any idea on this?

@chruff 

Also, i have successfully ran the configuration without any issues. It seems that email notification action are not working and thw workflow runs into an error

Task notification emails seems to be working fine.

Please advise.

Thanks

This error is typically related to TLS settings.  In particular, it indicates that TLS 1.2 needs to be configured on the K2 server.  This lines up with your move to Exchange Online, as Microsoft is enforcing TLS 1.2 in order to allow communication between your server and their cloud.  

To resolve this, you'll need to add the missing registry keys from this KB to the K2 server's registry: https://community.nintex.com/t5/Technical-Issues/K2-and-TLS-1-2-Support/ta-p/124200.  Afterward, restart the K2 server, and then attempt to 'Retry' these failed workflow instances from K2 Management.  This will need to be done on both of the Production servers.

hi @chruff we have Windows 2016 so it is enabled by default. 

Any advise on this?

Does the following Keys exist in the registry on the K2 Server?

HKLM:SYSTEMCurrentControlSetControlSecurityProvidersSCHANNELProtocolsTLS 1.2Server

HKLM:SYSTEMCurrentControlSetControlSecurityProvidersSCHANNELProtocolsTLS 1.2Client

HTH

Vernon

thank you all, updating the registry worked in my case.