This week, Microsoft warned Microsoft 365 email senders that outgoing messages must be authenticated. The move comes as Google recently announced stricter anti-spam rules for bulk senders.

“By setting up email authentication for your domain, you can reduce the chance of your messages being rejected or marked as spam by email service providers such as Gmail, Yahoo, AOL, Outlook.com,” said the Microsoft Defender for Office team. 365.

“This is especially important when sending bulk email (large amounts of emails) because it helps maintain the reach and reputation of your email campaigns.”

Failure to comply with recently announced email authentication standards may result in emails being rejected or marked as spam.

Microsoft also warned that Microsoft 365 should not be used for bulk email; because emails that do not meet sending limits will be blocked by outbound spam controls built into Exchange Online Protection (EOP) or sent to special high-risk distribution pools.

Those wishing to send bulk emails should use their own in-house email servers or third-party mass mail providers to help ensure good emailing practices.

Organizations that wish to send bulk email via EOP must comply with the following outbound spam protection guidelines:

• When sending high-speed or high-volume email, be careful not to exceed the service’s sending limits. This includes avoiding sending emails to a large number of BCC recipients.
• Avoid using addresses from your primary email domain as the sender for bulk email; this may affect normal email delivery from senders in the domain. Instead, consider using a dedicated subdomain just for bulk email.
• Ensure that email authentication DNS records, including SPF, DKIM, and DMARC, are configured on all custom subdomains.

However, Microsoft warned that “even following these guidelines does not guarantee delivery.” If your email is bouncing in bulk, please send it through a local or third-party provider.”

Redmond’s warning comes as Google announced new anti-spam guidelines targeting Gmail users who send more than 5,000 emails each day.

Starting February 1, 2024, Google will require senders above this threshold to use SPF/DKIM and DMARC email authentication for their domains. This measure aims to strengthen protection against email spoofing and phishing attempts.

Additionally, bulk senders must offer Gmail recipients a one-click option to unsubscribe from commercial emails and promptly process unsubscribe requests within two days.

As part of this anti-spam effort, Google said it will also closely monitor spam thresholds and if bulk senders are detected, it will flag their emails as spam to protect users from unwanted and potentially harmful messages.

“If you are not suitable [..]your email may not be delivered as expected or may be marked as spam,” warns Google. Source