Does the Crossware Service Support Message Recall? YES

Microsoft have confirmed that they do not support Message Recall when the email is routed through a 3rd party connector (in  Case #:26415836).
However, Crossware does have a solution around this:

Crossware Solution

Requires the creation of a Transport Rule, enabling Message Recall to work as expected.
Follow the below steps:


Configuration Steps

1. From the Exchange Admin Center go to Mail Flow>Rules

2. Click on "Create a new Rule

3.  Select "More options"
4. Transport Rule Settings

Name: CrosswareMailSignatureByPass

Apply this rule if...

A message header...includes any of these words

Header: Subject

Includes these words: Recall

Do the following...

Modify the message properties...set a message header

Message Header: X-CWesigProcessed
header value: Y

5. Click Save.

6.  Edit the Transport Rule> set the priority so that it is higher than the CrosswareMSTransportRule

7. Click Save

Further Documentation from Microsoft

Related Products: CMS M365