When sending and email from an application (i.e., Sage) via Outlook, you may see the below pictured prompt.
If clicking 'Allow' doesn't resolve the issue, please follow the below steps:
In Outlook, navigate to File - Options - Trust Center - Trust Center Settings -Programmatic Access
Change selection to 'Never Notify.'
See also, https://docs.microsoft.com/en-us/outlook/troubleshoot/security/a-program-is-trying-to-send-an-email-message-on-your-behalf.