Comcast Email Sending Error – Error Messages When Sending Email

by admin | Posted on Tuesday, October 12th, 2021

Xfinity is a renowned and well-established email brand that is known for its blazing fast internet speed. Apart from the Internet, it also offers an email service to its subscribers. Features and functions wise, the email service of Comcast is magnificent. It has a great user interface with easy-to-use features. However, there are some common issues that keep on causing trouble for Comcast users. 

Problems like Comcast Email Sending Errors keep on occurring from time to time. Such issues can be extremely troublesome if you are looking to send some urgent emails. In today’s post, we will discuss various Comcast Email Sending Errors along with their easy solutions. 

Why you are unable to send Comcast Emails?

The harsh reality of email services is that all of them are prone to some technical and non-technical errors. Comcast is not different. Many users grumble about the issues like being unable to send an email, can’t send emails, etc. Let’s discuss some of the major reasons why users have to deal with such a problem. 

    • Internet connectivity – You should have a stable internet connection in order to be able to send and receive Comcast emails. Those who are not connected to the internet might have to face an error while sending or receiving 
    • Size of the File – The size of the file you are trying to send should not be too big. In case you have to send a larger file then you can consider breaking it into multiple smaller files. 
    • Format of the file – Please note that the format of the file you are sending is supported. Please note that there are many file formats that are not supported by Comcast email. For example – you can’t send executable file formats like .apk, .exe, etc. through Comcast. 
    • Browser compatibility – The browser you are using should be compatible with Comcast. Those who are using an incompatible browser can face difficulties in sending Comcast emails. Thankfully, Comcast works fluently with most browsers like Chrome, Firefox, Internet Explorer, etc. 
    • Obsolete Browser – The version of the browser you are using should be updated. Users have to deal with various kinds of errors and issues while running their email account on an outdated browser.  
    • Add-ons and Plugins – Many users like to install add-ons and plugins to their browsers. However, these add-ons or plugins can be problematic as well. Some add-ons can also block you from sending Comcast emails as well. 

  • Not entering the email address of the recipient correctly – It is also possible that you are not being able to send the email because you are entering the email address of your recipient incorrectly.  

Different Comcast Error Codes and their solutions

There are different kinds of Comcast Error Codes that you might have to deal with while sending Comcast emails. Let’s some of these along with their solutions. 


  • Reason – This error occurs when you try to send an email from a dynamic/residential IP address within the Comcast domain.
  • Solution – To fix this error, you should make sure that you have configured the Comcast email account using the correct SMTP settings. 


  • Reason – The error code appears when a user tries to send an email from dynamic/residential IP space.
  • Solution – To resolve this issue you need to check the POP/ SMTP settings you are using. 


  • Reason – The Comcast filters have determined that email from your email server has been sent in patterns that are characteristic of spam.
  • Solution – Make sure the email you are trying to send doesn’t look like spam. Please note that Comcast has a very strict spam filtration policy. It will never let you send spam messages. In case you are not sending spam and still, receiving this error then you should Comcast support. 


  • Reason – The reason behind this problem is that the IP address from which you are sending is listed on the Spamhaus Zen. This is a list of addresses that are detected for sending a large number of spam. Comcast uses these lists to protect its users from receiving spam
  • Solution – In order to fix this problem you may try to send an email from a different IP address.  You may also request Spamhaus to remove your IP address from the list. 


  • Reason – In case you receive this error code then it is an indication that your IP address is listed on Return Path Reputation Network Blocklist. This is a list of IP address that send Spam messages to other users. Comcast also uses this list to keep spammers at bay. 
  • Solution – You should let the email service provider know about the outbound spam problem to avoid being blocked by Comcast in the future. You may also contact and request the Return Path to remove your IP address from this list. Your email service provider can also make this request on your behalf.

Other Non-Specific Comcast Email Sending Error Codes

Given below is the list of non-specific error codes that appear usually when you send a Comcast email. 

  • 421 – [Try again later] – It is a temporary error. It should get fixed automatically after some time. 
  • 421 – [Too many sessions opened] – This error occurs when more than 25 simultaneous connections try to connect per sending IP address.
  • 452 – [Too many emails sent on this session] – In the Comcast email, you can not send more than 1000 emails per session. This error results when that limit is exceeded. 
  • 550 – [Your message could not be delivered due to too many invalid recipients] – This error result when you are trying to send a message to too many invalid recipients. 
  • 552 – [Message size exceeed] – This error results when you try to send an email larger than 15 MB in size. 

We hope that you should be able to get rid of the Comcast Email sending error by using the information provided in this post. However, if you are still facing problems then you may seek help through Comcast Customer Service. 


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