Office 365 Exchange Online email system can silently quarantine emails from Sigma

If users have Office 365 Exchange Online for their email system, emails from Sigma can get silently quarantined by it.

When this happens the emails still show as having been delivered in our email logs, but the intended recipient may not be notified that the quarantining has happened. An Office 365 administrator will need to manually release the emails from quarantine so they can reach the recipient’s inbox.