In the BRS config file, edit the email thread setting. It should look like this:
<emailSenderThread type="PNMsoft.Sequence.WindowsServices.BRS.BuiltinTherads.EmailSender, PNMsoft.Sequence.WindowsServices.BRS" interval="10" sendRetries="10" siteUrl="http://[Sequence Server]/_layouts/" outlookWebService="http://serverName/SequenceInterfaces/" messageXsltFolder="C:\Program Files\PNMsoft\Background Runtime Service\Messaging\XSLT" messageLogosFolder="C:\Program Files\PNMsoft\Background Runtime Service\Messaging\Images" sendLogos="False" smtpServer="smtp.office365.com" smtpPort="587" username="yourusername" password="yourEncryptedPassword" enableSsl="true" useDefaultCredentials="false" isHtmlBody="True" attachmentLimitationSize="2048" />
You should add username, password, and enableSsl, and also set useDefaultCredentials to false.
The password is encrypted.
You can use the EncryptPassword utility: