Create a new mailing list in SmarterMail

Log into SmarterMail as administrator

Right-Click on the domain in question; Select Settings > Mailing Lists

Click New

Enter the list name (example@mydomain.com).

Choose the moderator i.e. the user which can user this mailing list.

Click on save button.

Now your list has been created, you'll want to add some Subscribers

Right-Click > Edit

Select Subscribers > Subscribers

Click Add Emails

Enter the recipient's one per line in the box given, Click Save

Now one can send the mail to all the subscribers at once using the single mailing list name example@mydomain.com