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I have set up a send-only server and I have tested it using mail-tester.com.

I get a 7/10, and I experience a majority of outlook/msn/hotmail inboxes sending my email to the junk folder. I do know Microsoft servers implement mitigation using black/whitelisting of IP-addresses, but I was hoping that maybe a 10/10 mail-tester score would help. I have already contacted Microsoft about them mitigating my IP, and they informed me I should try to score high on sender-reputation regardless of their policies.

I have DMARC/DKIM/SPF set up correctly, the only way I lose 3 points on mail-tester.com is because I do not have an MX Record set. From what I understand, an MX Record is not necessary for send-only email servers, however; Many posts/articles I've read online state that the lack of an MX-record is a big red-flag for recipient email servers.

My outgoing server address/FQDN is smtp.<my-domain>.ca, there is only the one server from one IP address that sends email, and the rDNS record is set up for it.

There is a lot of conflicting information online, and I don't want to clobber my DNS entries, what is the bare minimum MX record I should use?

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  • a bare minimum is just to set a mx even if it's not fetching mails, the sender will get a notification that the host is not responding – djdomi Apr 12 at 20:06
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Domains that send email but do not receive email will generate issues and/or be flagged as potential SPAM sources. Since you are sending email, you are expected to be able to receive bounce, unsubscribe and abuse emails. If you cannot receive emails, many mail servers will not accept your email. You will also soon find your server on blacklists.

MX records are not mandatory to receive email. If a zone does not have an MX record, then the A record will be used. Therefore, do not assume that a missing MX record means a send-only domain.

The following MX record states that no incoming email server is configured for the zone:

domain.example. IN MX 0 .

NULL MX Resource Record for Domains that Accept No Mail

Either accept a lower score or set up email receive functionality.

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  • Thank you, I'll look into configuring postfix/nginx to do this – David N Apr 12 at 20:15

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