When sending emails with my mailbox.org account, I occasionally receive errors like the following:

The mail system <xxxxxx@gmail.com>: host gmail-smtp-in.l.google.com[]
said: 550-5.7.26 This mail has been blocked because the sender is
unauthenticated. 550-5.7.26 Gmail requires all senders to authenticate with
either SPF or DKIM. 550-5.7.26  550-5.7.26  Authentication results:
550-5.7.26  DKIM = did not pass 550-5.7.26  SPF [bxm.at] with ip:
[] = did not pass 550-5.7.26  550-5.7.26  For instructions on
setting up authentication, go to 550 5.7.26
g4-20020a50d5c4000000b0056bf27dec57si5300544edj.105 - gsmtp (in reply to
end of DATA command)

Reason seems to be an error in my SPF/DKIM/DMARC setup. I am using the mailbox.org mail provider with my own domains (in this case bxm.at), which are hosted by all-inkl.com. After looking into the documentation of mailbox.org and all-inkl.com, I added the following DNS entries to the domain:

Name Type Data
mbo0001._domainkey CNAME mbo0001._domainkey.mailbox.org.
mbo0002._domainkey CNAME mbo0002._domainkey.mailbox.org.
mbo0003._domainkey CNAME mbo0003._domainkey.mailbox.org.
mbo0004._domainkey CNAME mbo0004._domainkey.mailbox.org.
  TXT v=spf1 mx include:mailbox.org a ?all
_dmarc TXT v=DMARC1; p=quarantine; rua=mailto:xxxxxx@bxm.at

The configuration looks fine now:

Just for reference, these were the values before my change:

Name Type Data
  TXT v=spf1 mx a ?all
_dmarc TXT v=DMARC1; p=none
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