Sending via ssmtp: 553 Relaying disallowed

Sending via ssmtp: 553 Relaying disallowed

I've set up MX records and verified the domain, but sending mail fails with the following log entries:
  1. sSMTP[28214]: Creating SSL connection to host
  2. sSMTP[28214]: SSL connection using RSA_AES_128_CBC_SHA1
  3. sSMTP[28214]: 553 Relaying disallowed
My ssmtp.conf is:
  1. root=borzhemsky@zoho.com
  2. mailhub=smtp.zoho.com:465
  3. rewriteDomain=zoho.com
  4. FromLineOverride=yes
  5. UseTLS=yes
  6. AuthUser=borzhemsky
  7. AuthPass=*******