Making -current machines accept mail from sendmail

Is there some special step to turn on dma so hosts
can receive email from a sendmail-using host? 

I've got three hosts using 12/stable (hence sendmail)
and a few more running -current (hence dma). The -stable
hosts report "connection refused" when sending to -current,
but -current has no trouble sending to -stable. 

On a fresh reboot I don't see any reference to dma in the
dmesg output, and ps -aux reports only busdma. 

Thanks for reading,

bob prohaska