The workflow fails to send email when configuring to use different From address in the Send Email step.
SourceCode.Workflow.Common.EWS: The e-mail address someone@xxxx.OnMicrosoft.com does not have 'send on behalf of' permissions on Exchange.
Granting 'Send As' permission to individual user account for the K2 Service account should do the trick. For this scenario, Exchange Online is integrated with K2 and Mod Administrator account is setup for it. The firstname.lastname@example.org needs to have 'Send As' permission, this can be done via Exchange Admin Center.
1. In the Exchange admin center, go to Recipients, then click Mailboxes.
2. Click Mailbox delegation. Then, under 'Send As', click on the plus icon and specify a delegated user to grant them the permissions. Save the settings.
This action may take up to 24 hours to fully complete within Office 365 and may require the person who was granted these permissions to log out and log back into the client they are using it.