Incompatibility between Sendmail and DMA

After upgrading from 13.3 to 14.2, sending emails from shel lscript, 
which had worked for about 20 years, stopped working.

The code looks like this:

mailto="mon mon-sms"
subject="DMA check"
msg="testing of DMA"

echo -e "$msg" | mail -s "$subject" "$mailto"

There are 2 space separated recipients, they are defined in 
/etc/aliases. And there is a quoted variable "$mailto". It worked for 
all the years I am using FreeBSD with Sendmail or Postfix. But it 
stopped on 14.x with DMA.

When I run the script it fails with: invalid recipient 'mon mon-sms'

I understand DMA does not like the quoted variable "$mailto", when I 
removed the quotes, then DMA can send message to both recipients, but 
the problem is we have tens of scripts on tens of machines and they will 
stop working when we upgrade them from 13.3 to 14.2.
Can this behavior be changed somehow to be the same as Sendmail?

The second problem is that alias in /etc/aliases cannot point to 
/dev/null. It also causes 'invalid recipient' error.

Are these known and documented incompatibility between Sendmail and DMA?

Kind regards
Miroslav Lachman