Why are emails to O365 recipients getting quarantined and how to fix?

Email marketer from Email Archive says that O365 uses content filters that scan emails for spam-like characteristics. Avoiding spam trigger words, using proper HTML formatting, and ensuring a good sender reputation can help prevent emails from being flagged as spam and quarantined.

Marketer from Email Geeks mentions Microsoft has aggressive filters, and this is usually the first sign you will start getting filtered on others.

Email marketer from Gmass suggests that maintaining a clean and engaged email list can help prevent quarantine issues. Regularly remove inactive subscribers and those who have not engaged with your emails in a while to improve engagement rates and sender reputation.

Marketer from Email Geeks says that if you don't have DMARC alignment, O365 assumes a DMARC policy and bulks non-aligned email.

Email marketer from StackExchange discusses the importance of setting up feedback loops (FBLs) to monitor and address complaints from recipients. By subscribing to FBLs, senders can identify users who mark their emails as spam and remove them from their mailing lists, improving sender reputation and deliverability.

Email marketer from Litmus emphasizes the importance of testing emails with different email clients, including Outlook/O365, before sending them to your audience. This can help identify and fix any rendering or formatting issues that might trigger spam filters.

Marketer from Email Geeks suggests checking the proximity of IPs experiencing issues, as it could be due to a bad neighborhood being listed. Also recommends checking SNDS.

Email marketer from Reddit shares that if you are on a shared IP space, your emails might be affected by the sending practices of other users on the same IP. If one user sends spam, it can negatively impact the reputation of the entire IP, leading to quarantine issues for all users sharing the IP.

Email marketer from Postmark emphasizes the importance of setting up DMARC, DKIM, and SPF records to improve email deliverability to Office 365 recipients. Properly configured authentication methods help Microsoft identify legitimate senders and reduce the likelihood of emails being quarantined or marked as spam.

Email marketer from Neil Patel Digital mentions that maintaining a good IP reputation is critical for avoiding quarantine issues with O365. Monitor IP reputation using tools like Sender Score and ensure IPs are not blacklisted. He also advises warming up new IPs gradually before sending large volumes of emails.

Expert from Spam Resource explains that a sudden drop in sender reputation can cause emails to be quarantined by O365. Contributing factors include sending to invalid email addresses, sudden increases in email volume, or complaints from recipients. Regularly monitor sender reputation and address any issues promptly.

Expert from Email Geeks advises setting up a domain hosted by O365 for customers to send test messages to in order to differentiate between global and individual issues. ESPs can address global issues but not individual filters.

Expert from Word to the Wise highlights the importance of proper email authentication and configuration, including SPF, DKIM, and DMARC, to improve deliverability to O365 recipients. They also suggest monitoring bounce rates, complaint rates, and engagement metrics to proactively address deliverability issues.

Expert from Spam Resource notes that Office 365's filtering is often more aggressive than other providers. They suggest senders should monitor their sending reputation closely and adhere strictly to email best practices, including authentication (SPF, DKIM, DMARC), list hygiene, and engagement metrics, to avoid being flagged as spam.

Expert from Email Geeks explains that O365 might have additional spam filtering for mail coming from IPs not their own MXs. Admins need to adjust these filters. Suggests checking BCL and SCL numbers to see if they are out of range.

Documentation from Microsoft Learn explains that emails are quarantined due to policies set by administrators or automatically by Exchange Online Protection (EOP) or Defender for Office 365. Reasons include suspected spam, phishing attempts, malware, or rule matches.

Documentation from Barracuda explains that one reason for emails being quarantined is if the sending IP address is listed on the Barracuda Reputation Block List (BRBL). They provide tools and methods to check if your IP is listed and steps to request delisting.

Documentation from Microsoft Learn details the process for administrators to release quarantined emails. This involves finding the message in the quarantine, reviewing its details, and then releasing it to the intended recipients. Admins can also report the message as not a threat to improve filtering accuracy.

Documentation from Microsoft Support explains how to add email addresses to safe sender lists in Outlook. Adding a sender to the safe sender list ensures that emails from that sender are not delivered to the junk folder. This is a user-level setting, so each recipient must configure it themselves.