Please extend your question with your platform details (distribution, version, ssmtp version, where did you installed from, etc.).
Regarding your config file:
/etc/ssmtp/ssmtp.conf
A few issues I see (which might or might not apply, depending on version):
- The hostname should have a FQDN (fully qualified domain name), else
Outlook (or Gmail, Yahoo and others) might reject it. You could try
adding one.
- You seem to be missing "AuthMethod".
- Some say that UseTLS and UseSTARTTLS exclude each other, others place both settings. You could try swaping between those options.
Example:
root=myemail@outlook.com
FromLineOverride=YES # usually goes with root
mailhub=smtp-mail.outlook.com:587
rewriteDomain=outlook.com # shouldn't be needed if you are not overwriting from, but doesn't hurt
AuthUser=myemail@outlook.com
AuthPass=mypassword
AuthMethod=LOGIN # could be plain or cram-md5 for ex.
UseTLS=Yes # this one might be yes or no
UseSTARTTLS=Yes
hostname=sierra-test.domain.com # full domain here, might help
You do have to keep in mind that if you enabled 2FA (two factor authentication) for you email/account, you will need to validate it before it allows you to send email.