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3 Messages

Tuesday, October 24th, 2023 2:24 PM

E-mails being rejected by AT&T


We are a software company with software that many clients use. This software includes functionality for e-mailing customers, whether individually or through automated marketing campaigns (also via automated processes like purchase confirmations). We've received 3 reports in the past month from clients receiving rejected e-mails to,, e-mail addresses and really need this to be resolved. Would someone please help with getting this issue cleared up? We have attempted to write to the [email scrubbed]t address provided in the rejection message but receive no response.

This is the mail system at host


I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below.


For further assistance, please send mail to postmaster.


If you do so, please include this problem report. You can delete your own text from the attached returned message.


                   The mail system


<>: host[] said:

    553 5.3.0 flpd570 DNSBL:RBL 521< >_is_blocked.For assistance

    forward this error to (in reply to MAIL FROM


Accepted Solution



26.2K Messages

4 months ago

Hi @AlbertGomezCB ,
We want to help. Let’s meet in a Direct Message on this. Please check your Direct Message Inbox (it’s the chat icon next to the bell icon in the upper right corner of the forums).


AT&T Business Social Media

3 Messages

4 months ago

@ATTBusinessCare, I came across old posts from you instructing people with this issue to private message you, however I don't have the option to do so anywhere on your profile.

3 Messages

4 months ago

Hello @ATTBusinessForums, I do not see this chat icon; I have the notification bell at the top right corner but only my profile icon is to the right of it, and navigation links to the left of it. Edit: I found the chat icon by navigating away from this forum post to my profile first


3 Messages

2 months ago

hi, @ATTBusinessForums,
I am currently facing an below error when trying to send emails. 
5.3.0 alph732 DNSBL:RBL 521
It appears that our server's IP address is being blocked by the AT&T mail servers. we kindly request your assistance in  solving the issue .

3 Messages

2 months ago


I have not heard back from anyone on this post. Can someone please reach out?

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