We dont and i have not seen plans for the GWIA, DKIM is supported in SMG so you might look into this 

But it feels a bit of an overkill to install SMG just for this.....

SMG can do a lot more then GWIA to prevent spam and with the policies for in and outbound mail you have a lot more controle over what comes in and what goes out. Diethmar can tell you a lot more about this 

We use SMG for GW web now as well to do the attachment and soon the message scanning 

We use SpamAsassin with GroupWise and are quite happy with that. The need to add an extra, expensive product will just fuel the discussion to switch to O365 or Proton.

If you have postfix with spamAssassin also DKIM can be configured, i cant make it better then it is as GWIA does not do this but we have SMG however this also might be an alternative

We have developed our own SA interface for GW, using the 3rd party folders. Not using postfix. I will look into OpenARC for now. So, basically use something like PostFix and have GW send all outgoing mail through it or implement ARC through the 3rd party folders.

edit: community.microfocus.com/.../gwia---configuring-to-use-a-postfix-server-to-send-outbound

I have a suggestion: Why not implement support for the sendmail "milter" protocol in GWIA. That is not just for sendmail but also for postfix. The milter protocol is used for mail filters and readymade implementations exist for spam filtering, DKIM, ARC etc.

yes Anders, we must place a beautiful multi-color ARCenciel over Groupwise to become the best protection (Arcentiel=Rainbow) in both direction,, internaly and externaly