It's a somewhat useful article, but reads like a marketing FUD piece by Postmark.

Most of these things have been essentially mandatory for Google for quite a while now. I'm not so sure about Yahoo so perhaps the article conflates the Google/Yahoo joint announcement with all of these things.

I did, however confirm on the previously-linked Google and Yahoo pages that they are changing it in February and it's not just for bulk senders (although many articles about it focus on that).

In addition to the requirement that apparently came into place in December 2023 to "Use a TLS connection for transmitting email", Google state:

"Requirements for all senders

Starting February 1, 2024, all senders who send email to Gmail accounts must meet the requirements in this section.

• Set up SPF or DKIM email authentication for your domain.
• Ensure that sending domains or IPs have valid forward and reverse DNS records, also referred to as PTR records.
• Use a TLS connection for transmitting email.
  
• Keep spam rates reported in Postmaster Tools below 0.10% and avoid ever reaching a spam rate of 0.30% or higher.
  
• Format messages according to the Internet Message Format standard (RFC 5322).
• Don’t impersonate Gmail From: headers. Gmail will begin using a DMARC quarantine enforcement policy, and impersonating Gmail From: headers might impact your email delivery.
• If you regularly forward email, including using mailing lists or inbound gateways, add ARC headers to outgoing email. ARC headers indicate the message was forwarded and identify you as the forwarder. Mailing list senders should also add a List-id: header, which specifies the mailing list, to outgoing messages."

Yahoo state:

"Requirements for All Senders:

• Authenticate your mail
• Implement SPF or DKIM at a minimum
• Keep spam complaint rates low
• Keep your spam rate below 0.3%
• Have a valid forward and reverse DNS record for your sending IPs
• Comply with RFCs 5321 and 5322"

Gavin