Why your emails are going to spam

First, work out which problem you have

"Going to spam" covers three quite different situations, and the fixes have nothing in common:

• Mail is bouncing. You are getting non-delivery reports. The bounce text usually names the reason, and at Outlook.com 550 5.7.515 means authentication specifically. This is the most fixable case because the error tells you what is wrong.
• Mail is delivered to spam folders. Nothing bounces; recipients find it in junk. Often authentication, often reputation, and telling them apart needs a message's headers.
• Mail is not arriving at all, silently. Sometimes filtering, sometimes a routing fault of your own, and occasionally mail that never left.

Configuration faults that cause filtering

• Two SPF records. Makes SPF return permerror. Very common, and invisible unless you look.
• SPF over ten DNS lookups. Same result, and it can happen without you changing anything.
• No DMARC record. Above their thresholds, Gmail, Yahoo and Outlook.com all require one.
• Sending platform not authorised. A new tool sending as your domain that nobody added to SPF, or that signs as its own domain so DMARC alignment fails.
• A revoked DKIM key. An empty p= value in a selector record. Every signature with that selector fails.

What configuration will not fix

If your authentication is already correct, the problem is not in your DNS, and no amount of further DNS work will change it. The usual causes are reputation on the sending IP or domain, complaint rates from recipients marking mail as spam, sending to addresses that no longer exist, or content patterns. Those need changes to how and to whom you send.

This is worth saying plainly because the deliverability industry is full of people who will sell you configuration work for a reputation problem. Run the scan: if it comes back clean, spend your effort elsewhere.

The fastest way to know

Send one message to a mailbox you can read, open the original, and paste the headers into the analyser. The receiving system records exactly what it thought of your SPF, DKIM and DMARC. That is a definite answer in about a minute, and it is free.