Is an MX-record required on a domain to send mails only?

Consider the following scenario:

  • I have a online-shop that sends mails with
  • There are no MX-records for as no mail to this domain is wanted
  • There is a valid SPF-record for

To be sure that mailservers will accept from, is a MX-record requried for or not? (In concerns of anti-SPAM systems)