550 5.7.509: your mail fails DMARC so the receiver rejects it outright
550 5.7.509 means the receiver could not align SPF or DKIM with your From domain. Here is how to fix DMARC alignment for Exchange mail flow.
550 5.7.509 means the receiver could not align SPF or DKIM with your From domain. Here is how to fix DMARC alignment for Exchange mail flow.