Sending an SMS via Microsoft Outlook or OWA.
To send an SMS (TXT message) simply create an "email address" in the following format;
where to the left of the @ symbol you are just inserting the recipient's mobile phone number and any applicable country codes or area codes.
For convenience it is a good idea to add this address as an alternative email address in your Outlook Contacts for that person so you always have it handy.
You can use this service to send an SMS to multiple recipients just as you would an email.
This video shows you how to send emails in Outlook;
This video shows how you to send a broadcast SMS with personalised content (first name etc).