smtp bounce code
550 5.7.509Message not accepted: DMARC failure
what to do
Keep the address, fix your side
The recipient's server enforces DMARC and your message did not pass. Nothing to do with whether the address exists.
What the server is telling you
Exchange Online checked your From domain's DMARC policy, found quarantine or reject, and your message failed both SPF and DKIM alignment.
Next steps
- →Do not suppress the address.
- →Align SPF or DKIM with the domain in your From header.
- →Sending through a provider often means alignment is set on a subdomain, which is fine as long as it matches.
Commonly returned by: Microsoft 365
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