Why do emails from outlook sent to gmail go to Spam?

To help narrow down the cause, could you please clarify a few things? Does this happen with every Gmail recipient, including people you've emailed before, or only certain recipients? Are you sending from an @outlook.com, @hotmail.com? Has this always happened, or did your emails previously reach Gmail inboxes normally?

Gmail often displays a warning at the top of messages in the Spam folder explaining why they were flagged. If possible, ask one affected recipient to open your message and check whether such a warning appears. Sharing its exact wording could help identify whether this is an authentication, sender reputation, or recipient-specific filtering issue.

Hi John,

Emails sent from an Outlook/Hotmail account landing in a Gmail recipient's spam folder usually happen due to a few common triggers. Here are the main reasons why Gmail might mark your messages as spam and how you can fix it:

Common Reasons

• Custom Domain / DNS Records Missing (SPF, DKIM, DMARC): If you are using a custom email domain through Outlook, Gmail requires proper authentication records (SPF, DKIM, and DMARC) set up in your domain’s DNS. Without these, Gmail automatically flags incoming mail as unverified or suspicious.
• Email Content & Formatting Triggers: Including short links (like Bitly), excessive images relative to text, spammy phrases ("Free", "URGENT", "Click Here"), or heavy HTML code in signatures can trigger Gmail's automated spam filters.
• Reputation or Blacklisting: If your IP address or custom domain was flagged for sending bulk mail or previously flagged by recipients as spam, Gmail’s security algorithms will automatically route your emails to the spam folder.
• New / Fresh Account: If your Outlook account is very new, Gmail has no established sender history or reputation for it yet, making its filters more cautious.

Here's the possible workarounds to Fix It

• If using a custom domain: Ensure your domain registrar has valid SPF, DKIM, and DMARC DNS records published.
• Ask recipients to mark "Not Spam": Have your Gmail recipients open your email in their Spam folder and click "Report not spam" (or add your email address to their Google Contacts). This quickly trains Gmail’s filters to recognize your sender profile as trustworthy.
• Simplify your signatures and links: Avoid heavy link shorteners, large embedded image attachments, or promotional phrasing in your signature or message body.
• Avoid mass emailing: If sending to multiple people, send individual emails rather than large, un-blinded recipient lists.