What the Xfinity(Comcast)-to-Yahoo Transition Means for Email Senders & Deliverability Professionals

Starting June 2025, Comcast’s email service (comcast.net) is being phased out and replaced by Yahoo Mail. This change will happen gradually through 2026 based on their announcement, but what senders, ESPs, and deliverability teams need to know?

Let's start with the basic.

All @comcast.net email addresses will be gradually migrated to Yahoo Mail, with users retaining their existing comcast.net addresses. The transition will occur in phases, and affected users will receive a 30-day advance notice before their move. Once a recipient accepts Yahoo’s Terms of Service and Privacy Policy, Yahoo becomes the new email provider for that mailbox, handling all future email delivery and filtering (yes, their spam folder as well).

Key Implications for Senders

1. Spam Filtering Will Now Follow Yahoo's Rules

Once a user migrates, Yahoo’s anti-spam and filtering systems take over.

Expect different inbox placement behavior than you may be used to with Comcast.

Reputation and engagement history under Yahoo will now matter more.

2. No Email Forwarding

If your recipients were forwarding their Comcast emails elsewhere, that forwarding stops after migration.

Delivery errors may rise temporarily if users haven’t completed their transition or updated third-party clients.

3. Changed IMAP/SMTP Settings

Once users switch to Yahoo Mail, they must update third-party clients (Outlook, Apple Mail, etc.) with new Yahoo settings.

If they don't, your message/newsletter/survey, etc. may bounce or be undelivered during the transition period.

As Comcast begins migrating its @comcast.net email addresses to Yahoo Mail, senders and ESPs should be aware of several risks that may impact deliverability and engagement.

One of the most immediate concerns is a sudden spike in bounce rates for comcast.net addresses, especially during the switchover windows when users may not have completed the transition or updated their mail client settings. In addition, senders may observe unusual drops in open rates, largely due to Yahoo’s more aggressive spam filtering algorithms, which differ from Comcast’s historical filtering behavior.

There’s also the potential for engagement delays, as some users might be temporarily locked out or slow to reconfigure access to their inboxes via third-party apps (such as Outlook or Apple Mail) after the migration.

What Should Senders & ESPs Do?

To stay ahead of potential issues, senders should take proactive steps. Start by closely monitoring bounce messages from @comcast.net recipients. These may provide early signals of access or filtering problems during the transition.

In addition, this is a great time to clean up your lists by suppressing long-inactive @comcast.net subscribers or triggering re-confirmation campaigns. Yahoo heavily weighs engagement in its filtering, so fresh consent and activity can make a difference.

Good to Know

It’s important to note that only @comcast.net email addresses are affected by this transition, no other Comcast or Xfinity services are impacted.

There are also technical limitations to be aware of: Yahoo will only migrate up to 4,100 folders and 10,000 contacts per mailbox. Anything beyond these limits will be trimmed or consolidated. Additionally, email attachments larger than 25MB will not be migrated — a detail that could affect archived content, re-engagement emails, or large support messages.

This migration is a big shift for senders who deal with comcast.net users. While addresses remain the same, behavior, filtering, and expectations will change. Stay proactive, monitor engagement, authenticate your mail, and prepare for Yahoo's inbox logic to take over.

Originally published on Moosend.