Recalling messages with Opensense signatures

Overview

Email recall is a Microsoft Outlook feature that lets senders try to remove a message from a recipient’s mailbox after it has been sent. Recall is not guaranteed, and has several limitations, especially when mail is routed through connectors or processed by third-party providers. While Opensense applies email signatures seamlessly, message recall is generally incompatible with server-side processing methods, and shouldn’t be relied on.

How email recall works today

Microsoft 365 now uses Cloud-based Message Recall. You start a recall the same way as before, but Exchange Online, not the recipient’s Outlook, finds and deletes the original message.

Where you can start a recall

Classic Outlook, new Outlook, Outlook on the web, Outlook for Mac, and Outlook for iOS and Android.

Options

Recall the message deletes the original email from the recipient's mailbox. Replace the message deletes the original, and sends a corrected version.

Recipients

Recipients in your organization. Recipients in another Microsoft 365 organization only if that organization has added yours to its cross-tenant recall allow list. Messages sent over the internet can't be recalled.

Read messages

Your admin decides whether messages that were already read can be recalled.

Results

A Message Recall Report email arrives within a few minutes, with a link to the recall status for each recipient. Exchange Online keeps trying for up to 24 hours.

For details, see Microsoft’s Recall or replace an email message that you sent and Work with Cloud-based Message Recall.

Recall and server-side signatures

Microsoft’s guidance for services that route all email through them, as server-side signature methods do, is that Cloud-based Message Recall supports messages within your organization that route out to such a service and back into Exchange Online for delivery. For this to work, the recall message headers must stay unmodified on the round trip, and the outbound and inbound connectors to the service must be configured properly.

Classic recall depended instead on the SearchKey MAPI property to identify the message in the recipient’s mailbox. When messages were routed through connectors (as is common with server-side solutions), the SearchKey could be altered, which made the recall fail. Microsoft confirmed this as a limitation of using connectors to route mail to third-party services. It applied to all server-side solutions, including Opensense.

Don’t rely on recall

Whichever recall your organization uses, treat it as best effort. If a message must not reach a recipient, don’t count on recalling it.

Classic recall (before Cloud-based Message Recall)

Before Cloud-based Message Recall, recall ran in the recipient’s Outlook. Classic recall was a legacy Microsoft feature with limited reliability, especially in modern cloud environments, or when using server-side email enhancements. It had these rules:

• Both the sender and the recipient had to use Microsoft 365 or Microsoft Exchange accounts in the same organization.
• The recipient had to use Outlook, and have it open, when the recall was attempted.
• The message had to be unread. A message that had already been read couldn’t be recalled.
• The recipient’s Outlook settings (like rules, or additional mailbox configurations) could make the recall fail.
• Messages to external recipients (outside your organization) couldn’t be recalled.
• Mobile apps and web-based versions of Outlook didn’t support starting a recall.

For how the SearchKey works, see Microsoft’s MAPI record and search keys.

What’s next

• How does Opensense work with Microsoft 365?: how email routes through Opensense.
• Fixing email deliverability and spam issues