Your Comcast email has stopped working. Maybe webmail won't load, your password keeps getting rejected, or messages have quietly stopped arriving in Outlook or Apple Mail. Almost every Xfinity Mail problem comes from a short list of known causes.
Most issues fall into a few groups: a service outage, a password or security setting, a mail app configuration detail, or the biggest change right now, the ongoing move of comcast.net email to Yahoo Mail. The fastest, most common fixes come first.
Work through them in order. The first checks take seconds, and there is no point reconfiguring a mail app while Xfinity itself is having an outage.
Check for an Xfinity Outage First
Before you change a single setting, rule out a problem on Xfinity's side. If there is an outage, nothing on your end will help.
Open the Xfinity Outage Map and sign in with your Xfinity ID to see whether an outage affects your address. You can also sign in to the Xfinity app to see outage details, including the estimated time to fix, or text OUT to 266278 (COMCST).
If an outage is shown, wait it out. To get a text when service is restored, click Request Text Updates in the outage banner and enter your mobile number. No setting or app change will fix email during an outage.
Sign In to Webmail and Reset Your Password
Next, rule out a bad password. Go to connect.xfinity.com and sign in with your Xfinity ID and password, or open the Xfinity app and tap Check email. Xfinity also asks you to complete two-step verification with a push notification, face or fingerprint, or a code.
If sign-in fails, reset the password at xfinity.com/password. Enter your Xfinity ID, mobile number, or personal email address, click Continue, choose to get a code by text or email, enter the code, then create and confirm a new password. It must be 8 to 128 characters, include at least one number and a special character, and cannot contain your name or username.
If you don't know your Xfinity ID, go to xfinity.com/username to find it first. Once you can sign in to webmail, watch for an invitation to move to Yahoo Mail, covered later.
Turn On Third Party Access Security
If webmail works but Outlook, Apple Mail, Thunderbird, or your phone cannot connect, this setting is the usual cause. It is unchecked by default if you weren't already using a mail app, and while it is unchecked, setup in a third-party app fails with an error.
- 1.Sign in at connect.xfinity.com with your Xfinity ID and password.
- 2.Click the Gear icon in the top-right corner and choose Settings.
- 3.Click Security.
- 4.Check the box under Third Party Access Security to allow third-party programs to connect.
Xfinity warns that these programs could expose your Xfinity ID and password to fraud, and could read, download, and delete email for you. That is the trade-off for using any third-party mail app.
Enter the Correct IMAP and SMTP Settings
Wrong server names, ports, or security settings quietly break sending and receiving. For a residential comcast.net account that has not moved to Yahoo yet, use these values.
Incoming (IMAP): imap.comcast.net, port 993, with SSL on. IMAP is the better choice if you read mail on more than one device, because it keeps them in sync.
Outgoing (SMTP): smtp.comcast.net, port 587 with TLS. If sending fails, try port 465 with SSL. Turn on authentication for outgoing mail.
Incoming (POP, optional): pop3.comcast.net, port 995 with SSL. Port 110 is no longer supported.
Use your full @comcast.net address as the username for incoming and outgoing mail, with your Xfinity password. Do not use port 25, which is not supported. Do not use comcastbiz.net servers either. Those are for Comcast Business, not residential accounts. Also check that Third Party Access Security is turned on, or these settings will still be refused.
Move to Yahoo Mail If Your Account Was Migrated
This is the biggest recent change. Xfinity is inviting comcast.net users to move to Yahoo Mail in phases that started in June 2025 and run through 2026. The move is free and optional. You get an invitation by email or when you sign in at connect.xfinity.com, and you accept Yahoo's terms to switch. Your address, messages, folders, and contacts come with you. Once you accept, you cannot go back to the Xfinity Email platform.
After the move, sign in at login.yahoo.com with your full @comcast.net address (include the @comcast.net part) and your password, then read mail at mail.yahoo.com or in the Yahoo Mail app. If Yahoo doesn't recognize the address and you typed it correctly, your account has not moved yet. For a password reset before the move, contact Xfinity. After the move, use Yahoo's Sign-in Helper.
In third-party mail apps, change incoming mail to imap.mail.yahoo.com (port 993, SSL/TLS) and outgoing mail to smtp.mail.yahoo.com (port 465 or 587, SSL/TLS, authentication required). The comcast.net server settings no longer work for a moved account, which is why Apple Mail and other apps suddenly fail after the switch.
Yahoo recommends an app password for third-party mail apps. Open your Yahoo Account Security page, click Create app password under External connections, enter a name for the app, click Generate password, and use that password in your mail app. Do this in a browser you have used to sign in to Yahoo for several days in a row, not in Incognito mode, or it may be blocked.
Re-enable a Secondary Mailbox Disabled for Bad Credentials
If a linked account shows "Your mail account [email protected] was disabled due to invalid credentials," that secondary mailbox stopped syncing. Fix it from the primary user's webmail settings, not from My Account.
- 1.In the primary account's webmail, go to Gear > Settings > Accounts, not My Account > Users.
- 2.Click Edit next to the affected secondary account.
- 3.In the "Incoming server" section, re-type that account's current password.
- 4.In the "Outgoing server (SMTP)" section, set Authentication to As incoming mail server.
- 5.Click Save. The account should re-enable and the error should stop.
Clear a 421 Excessive Failed Authentication Lockout
If sending fails with "421 resomta-... .sys.comcast.net Excessive failed authentication," a device on your network (or one sharing your public IP address) keeps trying an old password, so Comcast temporarily blocks the IP. One bad device can lock out everyone on the same connection.
Find every computer, phone, tablet, and app that connects to your Comcast mail. Update the saved password on all of them, and remove then re-add any account that still holds the old password. If an account won't re-add, check that Third Party Access Security is on.
If you miss one device, it will keep triggering the lockout.
Free Up a Full Mailbox
Each Xfinity Email account comes with 10 GB of storage, and there is no option to buy more. When the mailbox fills up, you may be unable to send or receive email, and you may see a message that your mailbox has reached 100% of its quota.
In webmail, click the Gear icon to check the email usage meter. Use the Sort by menu to sort mail by size, download any large attachments you want to keep, and delete those messages. Then empty the Trash from the menu next to the folder, because deleted mail still takes up space until it is purged.
Recover Messages Hidden by Spam, Filters, or Blocked Senders
If mail simply is not arriving, it may be misfiled rather than lost. Open the Spam and Trash folders and look for the missing messages. If a legitimate one is in Spam, mark it Not spam so future mail reaches the inbox.
Open mail Settings and review your filter rules, deleting or correcting any rule that moves or deletes incoming mail. Check the blocked addresses list and remove the sender if it is there. Finally, confirm the mailbox is not full, since that can also stop new mail.
Fix Webmail That Will Not Load in Your Browser
When the webmail page itself misbehaves, the problem is often on your device. Clear the browser cache and cookies, close and reopen the browser, and sign back in. Make sure cookies are allowed for xfinity.com.
Temporarily turn off browser extensions, especially ad blockers, which can break the page. Update the browser to the latest version and restart it. Try a different browser, device, or network to see whether the issue follows one device, and restart your modem, router, and device to clear network glitches.
Keep the Account From Closing for Inactivity
Xfinity closes unused mailboxes. To keep yours active, sign in at least once every 24 months, either at connect.xfinity.com or through a mail app such as Outlook or iPhone Mail. Since January 2025, accounts inactive for more than two years get a 90-day window of notifications and are then closed.
If you got a closure notice, sign in through the Xfinity Email website before the 90 days are up to keep the mailbox. If you plan to let it close, download your mail first at export.xfinity.com, because a closed account's contents cannot be recovered. Former customers keep access only if they signed in through the Xfinity Email website in the 90 days before disconnecting service. New comcast.net addresses can no longer be created.
Frequently Asked Questions
Why did my password suddenly stop working in Outlook or Apple Mail?
A common cause is a recent Xfinity password change that was not updated in every mail app, which can also trigger a 421 lockout. Also check that Third Party Access Security is turned on. If your account moved to Yahoo Mail, the comcast.net server settings no longer work. Switch to Yahoo's servers and use a Yahoo app password.
Is there a Comcast or Xfinity email app I should download?
You don't need a separate email app. You can open your mail from the Xfinity app by tapping Check email, use webmail at connect.xfinity.com in any browser, or set up a third-party mail app with the correct server settings. If your account moved to Yahoo, use the Yahoo Mail app or mail.yahoo.com.
Should I use port 587 or 465 for sending?
smtp.comcast.net supports both. Try 587 with TLS first. If sending fails, switch to 465 with SSL. Never use port 25, which is not supported.
Why can I receive mail but not send it?
Check for a sending limit or a lockout. A single message can go to at most 100 recipients, you can email up to 1,000 recipients per day (after that, sending is blocked for the rest of the day), and a message cannot exceed 25 MB including attachments. A "421 Excessive failed authentication" error instead means a device is trying an old password, which temporarily blocks your IP address.
I have a comcastbiz.net address. Are the settings the same?
No. comcastbiz.net (imap.comcastbiz.net and smtp.comcastbiz.net) is for Comcast Business and is separate from residential comcast.net (imap.comcast.net and smtp.comcast.net). Do not mix the two server sets.
Will I lose my emails when my account moves to Yahoo Mail?
No. Your @comcast.net address, messages, folders, and contacts move with you. There are limits: up to 4,100 folders and 10,000 contacts transfer, folder names over 240 characters are shortened, and emails whose attachments total more than 25 MB don't move, so download those first.