Email from forum undelivered, return to sender

My website URL is: Domain removed by

What I’m seeing is: Emails from forum registration and notify of reply to a post are being returned to Domain [email protected] as undelivered mail, return to sender

Please describe what you SEE. For example, you could write steps to reproduce, copy-paste error messages or error logs, or share screenshots: Emails are being returned to sender as undelivered mail, see the snip of the returned email with error message below:

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.

host[] said: 553 5.3.0 alph775 DNSBL:ATTRBL 521< >_is_blocked.For assistance forward this error to [email protected] (in reply to MAIL FROM command)

**I’m using this software:**MyBB 1.8.22


Additional information: checked with

Link with results here Spam Test Result

I have used, the IP showed as a spam IP, I requested it be removed from the blacklist at Barracuda. That was the only place out of dozens that showed the IP as blacklisted, now at least it shows as not a poor rating. I also forwarded the email to [email protected]. I have a gmail address for the website, could that be the root cause of emails being returned? Gmail is kind of picky about emails being forwarded so that could be a problem.

All idea’s are welcome :slightly_smiling_face: a solution would be great!

I’m not trying to use the site email as a regular email, only for forum generated emails to users for registrant verification, reply to your post, you’ve received a PM notification, etc…

If you use php mail function, it can only be used for registration/activation emails.
Forwarding to Gmail (or most mail service) will not work (if you forward directly from your webmail address).
But using google STMP should not result in it being blocked. (Solution: Use google STMP). There is an article on this.

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From reading the articles I know outgoing php is heavily restricted. See the quote above, it’s only being used for registration/activation emails and those are returned as not delivered. I’ve read the knowledge base and so far nothing works, that doesn’t mean a solution isn’t there, it means it hasn’t been found yet.

Isn’t this the exact same error as you posted in your other topic? If so, please see my response there too.

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Yes it is the same error, it’s in the raw message of the returned email. I’ve done more research, found the correct SPF data and added it, I know things look clear and understandable to you @Admin, that’s not the case for me. I do try and figure things out for myself, and some posts of mine may be more to verify what I think is the right thing to do before I do it, I’m concerned about changing something, and making a problem worse than it was before.

I’ve been able to get a 9/10 on mail tester Spam Test Result, in reading through the knowledge base free hosting email, even from the site to users for registration/notification only may be iffy at best. There is no provision for adding DKIM or a pointer on a free host.

Thank you for following up on my post, thanks to the extensive knowledge base I’ve been able to get my mail test score to about as good as it will get.

At this point I’m not planning on adding the SMPT POP mail to my site, I may end up going to iFastNet Premium in the not too distant future. I have to see how the emails are working now that I’ve gotten to a 9 on the test mail application.

I hope the SPF changes will help to push your email across the spam threshold at

However, it should be note that while is a useful tool, a stamp of approval from them doesn’t mean every mail provider will accept your messages. All mail providers have their filters setup differently, and may use different spam filters and different blacklists to verify messages. And if has blocked our mail server IP, as the bounce mail implies, I’m not sure if this is enough.


I agree with you on whether or not a 9/10 score from email tester will change anything, it did help identify errors and issues. I referred the issue of the alleged spam IP to [email protected].

The paste below “The mail system” is the same error that’s been occurring when the email is returned. The snip below that is the response to the referral, they ask that I configure a unique pointer record that matches my servers A record. From what I’ve read that can’t be done on a free host, if things don’t clear up I’ll either try to work with the SMTP solution, or consider moving to iFastNet premium.

The mail system

<[email protected]>: host[] said: 553 5.3.0 flpd568 DNSBL:ATTRBL 521< >_is_blocked.For assistance forward this
error to [email protected] (in reply to MAIL FROM command)

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Thank you for taking the effort to contact ATT!

I’m not sure what they say is wrong with the IP address and the reverse DNS. The reverse DNS of the IP address points to, and this domain name correctly resolves to the IP address.

Or maybe the issue is that the mail server name doesn’t point to that IP address? I’m going to ask iFastNet to update this, it probably wouldn’t hurt to change this.


You are welcome @Admin, anything I think I can do myself to clear a problem I’ll do it. I believe what you state below may be the root cause (server name ‘’ doesn’t point to that IP address)

My MX records show associated with the random 9 character domain ending in The record associated with my domain is, I don’t know enough about it to say whether that could be a problem.

If there’s anything I have the capability of changing, please advise me what it is, and what it needs to be changed to. An option, setting, or entry in the iFastNet servers could be a root cause of email issues for other InfinityFree users too (wishful thinking on my part :thinking:)



You know this. You read the article where we clearly explain this, because you linked to it in your other topic. Stop involving MX records of unrelated domain names to it. Because they can never, will never and have never affected email sending on any other domain in any way, shape or form.

Could you please enlighten me why you still seem to believe this MX records for a completely different domain name is related in any way to your email sending issues?


I’m grasping at straws @Admin , you’re right I do know this :anguished:

The emails are sent without issue, it’s the receiving email server that suspects the email is spam. The sending server is responsible for providing correct information to the receiving server.

What I understand about email in general is the receiving server does various checks to validate an email. Is it legitimate, suspected spam, or somewhere in between? As far as I know that information comes from the sending server, I could be wrong, but that seems to be the way it would have to work to validate the sender.

I see in the returned email error message, and I see in the MX records. That is the sole reason I suspected the byetcluster entry in the MX records, you’ve made it clear and I’ve seen it in the knowledge base where it isn’t a problem.

I’ll put that thought to bed and won’t mention it again :zipper_mouth_face:

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@Admin, late note, after using to clean things up I’ve been testing my forum account activation emails using different email addresses. Those activation emails go through immediately to an or email, but are not delivered to an (ATT) email address.

That matches quite well with what we’ve seen so far: our system tries to deliver the message, but the mail server IP was blacklisted by AT&T, so AT&T blocks the message. Other providers may not have blacklisted the IP, so they do accept your message.

The DNS and reverse DNS for has been updated as well now. Can you please contact AT&T and see if this is enough to get them to stop blocking the messages from your website?


Thank you for getting the DNS and reverse DNS for updated!

I have forwarded the email from AT&T abuse back to [email protected] per the direction on their notification email. I’ve advised them I worked with the @Admin of my webhost, to address the issues they saw, and those issues should be resolved.

I asked they recheck and please remove the IP associated with from their blacklist. :crossed_fingers:

The time frame for that is 24 to 48 hours, (I sent the email at 2:31pm Sat. 2-22) I should receive another email from them when they’ve determined the outcome.

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The email trouble has been resolved after working with AT&T, and Infinity Free @Admin. The issue was auto-generated emails from my forum site for registration validation, reply to post, and PM notification emails were not being delivered to AT&T mail servers. Any forum members on AT&T servers never got an email, other email servers, and were fine, this was limited to AT&T email servers.

This took time, effort, and patience moving to a resolution, getting the correct information to the right people/organization(s) was what took time. The actual fix of updating servers and removing the block on the IP probably took 10 seconds, haha

Using the returned email error information message given, Admin was able to determine iFastNet servers probably needed updating. After getting those servers updated the email problem has been resolved, as an example of what the returned email with the error message looked like I’ve pasted it below.

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.

[email protected] host[] said: 553 5.3.0 alph775 DNSBL:ATTRBL 521< >_is_blocked.For assistance forward this error to [email protected] (in reply to MAIL FROM command)

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