Hello again! I’m not sure this is the best place to ask this question, but I’m starting here.
My question is in relation to the expected behavior of mail servers when a domain is configured with a DMARC DNS TXT record. For the sites I manage, I tend to configure SPF records with “-all” because I don’t want ANY other mail server to send mail on behalf of our domain, other than the servers listed in the SPF record. For the related DMARC record, I tend to specify a strict rejection policy and I have the DMARC reports being sent to an email account I monitor, so I can keep tabs on the mail server activity. So, the SPF record ends with “-all” and the DMARC record has a “reject” policy configured.
On a couple of domains I manage, I noticed strange mail server behavior. For the sake of discussion, I’ll use “mydomain.com” as the domain. I’ll receive an email message either in the spam folder, as blocked by SpamAssassin, or in the inbox where the “From” address and the “To” address are the same address AND the address is MY email address:
From: tomdkat@mydomain.com
To: tomdkat@mydomain.com
The message was sent to me from mail server aaa.bbb.ccc.ddd, which isn’t affiliated with my domain at all and that address wasn’t listed in the SPF record, for my domain.
Since the mail server for “mydomain.com” received the message from mail server aaa.bbb.ccc.ddd, why would “my” mail server receive the message? Sometimes, SpamAsssassin will trigger the “FAIL_SPF” rule and that pretty much flags the message as spam but I would have expected “my” mail server to reject the message entirely, based on the SPF record and the DMARC record configured for the domain.
In one instance, this happens in a shared hosting environment, so my domain’s mail server is shared by “everyone else” (lol). In another instance, the site is in a VPS and there’s only one site and one domain setup. It’s almost as if the local mail server “ignores” the SPF and DMARC records if the “From” address is in the domain the mail server manages.
Any ideas on what could be going on? Any recommendations for a better forum where I could ask this, if this isn’t the best place to ask?
Thanks in advance!