Deliverability Issues – All Emails Going to Spam Despite Proper Setup

Did you manage to get a copy of the email header for one of those sent to spam box? Specifically I need to review this section like in my example.

So you are using the exchange, your own domain brought to Msft 365, right? If this is newly set up, you might need to wait 24 hours yet for SPF, DKIM and DMARC configuration to take effect.

Also, have you had the chance to ask for the email header of the sent copy from the receiver's end, and see if it did specify failure for spf, dkim and/or arc?

One of our companies uses Zoho Campaigns to send marketing emails and we noticed a large increase in soft bounces this week. Upon investigation, we found that there is a custom return-path warning in the SPF reports. I found a spot in Zoho Campaigns where I could validate a custom return-path by entering a CNAME record into our DNS records.

We also received an email from Zoho regarding Microsoft's tightening of the rules for domains sending more that 5k emails per day starting May 5th, 2025. SPF, DKIM, and DMARC are mandatory and will bounce instead of getting flagged as SPAM.

We are new to this, so are currently warming up multiple addresses on multiple domains for marketing purposes. We also moved off of our "transactional" domain (our primary domain that the web app lives in and where business functions) and now use those dedicated marketing domains I'm warming up. We've seen some better results on the addresses in domains that have warmed up for at least two weeks, but I anticipate getting better results once they surpass 30 days, or greater, and get better reputation scores.

Good luck, this has been quite a challenge and an eye-opener for a guy that's spent his career keeping these out of inboxes. :)

Edit: Also, check your authentications (DMARC, etc.) by dropping your domain in here: Domain Health Check - Online Domain Tools - Blacklist, Email, Website, DNS - MxToolBox. Since you're not bulk sending, it's likely a config issue.

Hello,

To clarify: I'm using Microsoft 365 as my email provider, and I’m sending emails directly from Outlook — both the desktop app and the web app (https://outlook.office.com). The issue happens consistently across both.

The domain is newly set up but has valid SPF, DKIM, and DMARC records, and I’ve been warming it up gradually without bulk sending. However, my emails — even to known recipients — are still landing in their spam folders.

Hello,

I need to understand the set up a bit better -

Who's your email service provider? You said you are using a new domain and are sending email via Outlook (ms365) - to me, that means your email service provider is third party, but you set up your email via the Outlook email client app and emails were sent from the Outlook app, is that the case?

If that the case, typically the email client app is not the issue that can cause your emails to be marked as spam. I am interested in knowing - if you access your email address directly via the web, and send the email directly from there, is it still being marked as spam on the receiving end?