In Mail2Fax definitions we have two options:
fax.domain.com. When the email server receives one message for that FQDN, the message attachment will be forwarded to the FAX server that sends the FAX by the PSTN;
After update configurations you will be able to send Faxes from a workstation using a simple email client. At the workstation side just:
To: field insert number@fax_domain. Example 221121112@fax.domain.com;
.pdf file that will be the FAX;