When using the Send Message option from a roster page you will be directed to the Customer Search & Email report with that specific Team ID selected.
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From the Customer Search & Email you can utilize an existing Email Template or simply type your message in the Body. You can also filter the recipients down even further before clicking the Email button, if needed.

As long as you are sending a message to a roster that has less than 250 players the emails will be High Priority and won't be delayed.