The following screen appears when run [alternatives --config mta].
There are 2 programs which provide 'mta'.
Selection Command
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+ 1 /usr/sbin/sendmail.postfix
* 2 /usr/sbin/sendmail.sendmail
Enter to keep the current selection[+], or type selection number:
The asterisk (`*) indicates the option that the alternatives software believes is "best" and would use if auto mode is selected.