Miscrosoft has recently decided to embrace DMARC more explicitly, much like their email brethren, Yahoo, AOL, and Gmail. You may have started seeing bounce messages with the following reasons:
Hotmail / Outlook / MSN / Live:
550 5.7.1 The messages violates the DMARC policy of domain.tld (1b6c35a4-2c11-11e6-ab23-549f350a57e2)
550 5.2.0 54Qa1t0144ZKE95014QaMR Message rejected due to DMARC. Please see http://postmaster.comcast.net/smtp-error-codes.php#DM000001
550 5.2.0 54QF1t03z3oQ44H014QGZ3 Message rejected due to DMARC.
This is because Microsoft will no longer be accepting messages where the From domain is a Microsoft domain address and the message originates from a non-approved Microsoft mail domain server/service. This is a security measure they have implemented to help reduce potential address spoofing of their mail domains.
What this means: As of June, 2016, you can no longer send with the From address being anything from a Microsoft address when sending to a domain that checks DMARC before accepting mail.
What you can do: You will need to change the From address you use in emails to a non-Microsoft address. We recommend using one at your own mail domain, or one you control that is legitimate. You can then set the Reply-To field to be the original Microsoft address that previously was used in the From field.
What about these messages, are they lost? : Yes, any send with this bounce message is discarded and tracked as a Block. You will need to adjust your From address field settings, and then try resending from your side.
For more information, check out check out this article on the DMARC changes.