ISP Deliverability Guide: Comcast Xfinity

American multinational mass media, telecommunications, and entertainment conglomerate Comcast has somewhere north of 30 million customers with Xfinity residential broadband internet service. And while they don't publish numbers around what percentage of that subscriber base may have a comcast.net email account, it is very likely that some significant number of those customers do.

Email senders, in particular US-based email marketers selling to consumers (B2C), tend to see Comcast ranked somewhere around #4, #5, or #6 when it comes to ranking the number of comcast.net email addresses found in a typical email list. Comcast may not be in the top three mailbox providers, but they're still significantly represented, definitely in the top ten, and it's important for email marketing success to be able to reliably reach the Comcast inbox.

Here’s everything you need to know about how to successfully send email to Comcast Xfinity (comcast.net) subscribers, and how to troubleshoot deliverability issues that may arise.

Start With the Basics

Broadly speaking, Comcast's requirements are aligned with the modern email sender requirements put forth by Yahoo, Gmail, Apple, and Microsoft (MAGY). If you're looking for a starting point, review my MAGY Sender Compliance Guide first. Comcast requires TLS authentication and enforces email authentication requirements very similar to those updated sender requirements.

Also note that Comcast publishes a p=reject DMARC policy for the comcast.net email domain. This effectively prohibits sending email with a From address in the comcast.net domain unless you are using Comcast infrastructure. A reminder that it is bad form, and damaging for deliverability, to send your newsletter or marketing mail using a From address in a domain that you do not own. This is yet another reinforcement of that.

The Only Domain That Matters Is comcast.net

The only email domain hosting consumer mailboxes of Comcast users is comcast.net. This is a common point of confusion.

Note that comcast.com (and cable.comcast.com) are email domains reserved for employees and services of Comcast. They are not where Comcast Xfinity cable subscriber mailboxes are hosted. (It might be wise, in some circumstances, to prohibit comcast.com list subscriptions to mitigate this confusion, but note that doing so may block Comcast employees from signing up for your emails.)

The Transition to Yahoo Mail Is Coming (Eventually)

Comcast has announced that they are, eventually, getting out of the consumer mailbox hosting business. They are transitioning all comcast.net subscribers from their own hosted infrastructure over to Yahoo Mail infrastructure. When this is complete, comcast.net will effectively be another Yahoo Mail domain, and Yahoo Mail sender requirements and deliverability policies will apply.

How fast this will happen is unclear. The transition was announced in July 2025, and it is now October 2026, and no further announcements have been made. The MX records for comcast.net still point at Comcast infrastructure.

Xfinity's own support documentation says that customers will be invited to upgrade their email accounts to Yahoo Mail gradually through 2026, with invitations rolling out in phases. For senders, the practical implication is that you should plan for a future where comcast.net is governed by Yahoo's rules, but for now, you still need to understand and follow Comcast's rules.

APRF: A New Feedback Standard Comcast Supports

Comcast supports the APRF (Aggregate Performance Reporting) draft specification. APRF is sender feedback that shows whether or not your mail was delivered to the inbox or not, and helps you understand recipient sentiment, positive or negative, about your email sends. This is valuable data.

APRF works by tying reporting to your DKIM signatures. You publish a DNS TXT record at a specific location under your signing domain, and the mailbox provider uses that record to discover where to send aggregated daily reports. The reports are delivered in JSON format and contain placement and engagement metrics . To protect individual user privacy, APRF enforces volume suppression thresholds, so low-volume senders may not receive reports at all .

Comcast is the only mailbox provider to support this standard so far, as of October 2026. Google co-authored the draft, which signals strong long-term interest, but Gmail does not currently generate APRF reports. I hope others will add support in the future.

If you want to get started with APRF, Comcast is actively generating reports in production for senders who publish the DNS record. You can find the record structure and setup steps in the draft specification.

Comcast's Postmaster Page

Comcast has a Postmaster page, a site filled with information meant to enable senders to understand Comcast sender requirements, email policies and troubleshoot deliverability-related issues. It can be found here. This includes information detailing the different SMTP rejections that an email sender can receive when attempting to send mail to Comcast subscribers. If you're sending to Comcast and seeing trouble, this should be your first stop after checking your own authentication and infrastructure.

Getting Unblocked

For those senders finding their email blocked by Comcast, Comcast has a contact form where you can reach out to request unblocking. That form can be found here. Please note that Comcast makes it clear that if the SMTP rejection contains a different URL leading somewhere else, senders should follow that URL instead to see what unblocking process relates to that specific error. This form at the URL here is only for SMTP errors with the BL000000 blocking code.

Comcast uses multiple blocklists and reputation services in its filtering, and each has its own removal process.

Sending Limits

Comcast has published sending limits on its Postmaster page:

• Comcast allows 25 simultaneous connections per sending IP address.
• Comcast allows 100 recipients per message.
• Comcast’s allowed throttle rate is based on your sender reputation and authentication.
• Comcast says that the employ a limit of 1,000 messages an hour per netblock for senders using IPv6.

Comcast's rate limiting is reputation-based. The more authenticated and reputable your sending, the higher your allowance. Unauthenticated or low-reputation senders are likely to have a rougher time of it.

New IP addresses expected to send significant amounts of email to Comcast subscribers should start by sending low volumes of mail, increasing as time goes on.

ISP Feedback Loop

Comcast offers an ISP feedback loop, a feed sharing details of "this is spam" reports by Comcast users in response to email sent by a brand, company, or email platform. Email senders can sign up for this FBL here.

Note that a sender's email marketing platform may already be registered with this FBL and may already be processing complaints. Senders should check with their ESP, marketing or newsletter platform for guidance. For example, Salesforce Marketing Cloud indicates that they automatically enroll all clients in the Comcast FBL, so those senders may not need to sign up separately.

Also note that some FBLs do not send every single spam report back, so do not assume that this is the case. FBL reports are meant to help people become better senders by allowing them to identify which sends or data sources may be problematic based on elevated spam complaint rates. FBLs are not meant to enable "list washing," where senders simply unsubscribe complainers but continue to send unwanted or unsolicited mail.

Warm Up Your IP and Domain

Like with many mailbox providers, IP and domain warming is a best practice when sending to Comcast subscribers. Don't just show up on day one and send to 500,000 Comcast addresses all at once. Warm up your IP and domain by starting small and building up volume (and reputation) over time.

Deliverability vendor Validity includes more information and recommended IP warming volume for Comcast in their own Comcast Deliverability Guide, which can be found here.

Avoid "warmup services" that simulate engagement with non-human opens and clicks. Validity and others (likely Comcast, too) consider this a bad practice and if identified, reputation (and inbox placement) can suffer as a result.

What Comes Next

Comcast runs its own email infrastructure with its own rules, and email senders looking for deliverability success will want to understand and abide by those rules. That means authentication, that means reputation-based sending, that means watching your complaint rates and respecting the feedback loop, and that means not trying to shortcut your way to the inbox with tricks that don't work.

The transition to Yahoo Mail will eventually change things. When comcast.net mailboxes fully migrate to Yahoo's infrastructure, Yahoo Mail's sender requirements and deliverability policies will apply, and the Comcast-specific guidance in this guide will become historical. But until then, and possibly for quite a while longer, Comcast is its own ecosystem with its own expectations.

If you're sending to Comcast subscribers and you're not sure whether you're doing everything right, start with the fundamentals: authentication, permission, engagement, and list hygiene. Those are the things that keep you in the inbox regardless of who is running the infrastructure.

Click here to view the whole series of Spam Resource ISP Deliverability Guides.