Validation of e-mails is provided. An e-mail is received. A sender of the e-mail is determined. A message posting service account that is associated with the sender is identified. The message posting service is queried for a first hash value that corresponds to the e-mail based, at least in part, on the account. A response is received from the message posting service. Whether the account includes the first hash value is determined based, at least in part, on the response. The e-mail is or is not validated based, at least in part, on the response from the message posting service.