E-mail to SMS being blocked due to suspected SPAM

I work for a trucking company, and we use e-mail to SMS to send out dispatch messages to our drivers for load information. Drivers can then reply to those messages to have conversations with dispatchers who operate via e-mail.

This has been working for years; however, as of 3/26/2018, it seems our entire domain has been blocked by T-Mobile servers. E-mails sent to are rejected with 550 errors. I have tried sending as plain text, e-mail, short, long, with picture, and just about every way I can think of, but it's always blocked. Messages sent to all other mobile carriers are still going through just fine.

I have tried calling support, but no lower-level techs seem to even understand what E-mail to SMS is, and they just exhaustively try things that are specific to one individual phone. They supposedly escalate the issue, but we never hear back. I am desperately searching for someone within T-Mobile who can actually tell me why my domain is suddenly being blocked. This functionality is critical for our drivers to do their jobs; I'd prefer my answer to those drivers not be "sorry, find another carrier" as they keep asking us why their messages are failing while all the non T-Mobile users are moving along just fine.

@srickar​ - I've seen where you've been super helpful to some people; is there any chance you could help us out, too? I can PM you specifics.


Best answer by tmo_chris 5 November 2019, 00:21

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Userlevel 3
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Common reason messages are rejected are attributed to a sender domain setting for DKIM. There’s other settings to be aware of like SPF, DMARC, in addition to DKIM. We send a rejection message specifying the denial reason on all security failures. Please check Postmaster/SMTP rejection response for the final disposition.

I use these 3rd party tools to verify DKIM. The best way to see your DKIM key, is to send yourself a message and review the header properties of the message.








The published purpose of these security settings is to cut down on spoofing of another domain and to specify which ISP hosts are allowed to send email on behalf of a domain. Sometimes settings are not updated or the sending entity is intentionally not welcomed to send mail on another domains behalf (security lockdown).

  • Was there a recent expansion or change in SMTP email services for a corporation?
  • Is someone trying to send email on behalf of another affiliated company?
  • Has the IT admin performed a health check to verify IPs are still current in SPF record?

I commonly see this where an associated business or government entity tries to borrow email services but the SPF/DKIM/DMARC expressly forbid based on the published DNS. Our system is honoring the published DNS as to the current specs to reject outsider attempt.

Hope this helps others.

Userlevel 2

I just started sending text from laptop to people rather than phone, if I can.  (I have a hand tremor that makes "typing" text hard.)  Dictation to phone only works some of the time.   No problems so far.

  I might be wrong - it would appear text can be handled/processed via TM or Google.  (I have a Pixel phone.)

Hello @srickar

It looks like you are the one to talk to for these 550 errors.

I too have a particular person (my boss) that is unable to send me email to text messages due to being blocked.

I have requested a follow and awaiting approval.

Please let me know what information you may need so that we can resolve this.

Thank you!

Userlevel 3
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PM sent.

Userlevel 3
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I blocked that yesterday because it was flooding our SMTP connections. This type of automation traffic should ideally be sent over a shortcode provider due to the characteristics of the message. This front end interface is not designed to accept that amount of traffic for an enterprise. Please see section 4.2 pertaining to enterprise traffic volume and why dedicated shortcode gateways are setup to handle this.

Even if I did not block, the messages were easily exceeding rate control connection limits which is generous. Also, the messages sent to each device was causing flooding to device delivery to the point devices couldnt acknowledge the messages fast enough.

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I have removed the outright block, but please note that exceeding rate control volume is still possible and I cant circumvent since rate control is a global setting. For this type of A2P automation, the traffic should move to a shortcode provider like Syniverse, Twilio, Sybase, etc. These dedicated routes have different anti-spam policies for vetted traffic and perform ENUM lookup automatically to find the right carrier owner.

Since you are using email, if a subscriber ports between different carriers, you are essentially emailing a stale address which ENUM lookups are performed in real-time by the shortcode operator. Also, if a subscriber were to swap numbers and a former number is now assigned to a new user who's getting these email blasts, they could report it to FCC for TCPA violation. Something to consider as to why enterprise compliance is crucial these days. Thanks.


Good afternoon!

We seem to have found our way on to the T-Mobile blacklist, this is what we are getting:

"recipient-domain": "",

"id": "8y7NCQN5T_iaNTMnARFxIQ",   

"campaigns": [],

"reason": "blacklisted",

"user-variables": {},

"flags": {

"is-routed": false,

"is-authenticated": true,

"is-system-test": false,

"is-test-mode": false

Our service sends emails to text messages for Doctors and it has been working perfectly for about a year to one of our clients who is a T-Mobile user, but last Friday we started getting bounce back emails with that reason code.

Would you be able to remove from your blacklist?

I would very much appreciate it!



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Found the reason. That email address is using "postmaster". It's such a generic email user name that it was blocked for unrelated use by spammers. ";;; etc. Please change the presented configuration so that it's not so generic.

Nice!  Thanks for that, I'll see if we can get that changed by our mail host.

Much appreciated!


Thanks @srickar​. I believe it worked. I just used test2 instead of test 😀.

For anyone else wondering your sender has to be the same as the true sending address. email to rejected for banned content

"IMPACT: Customers may be unable to receive messages to messages to their address. To help aid the attack against SPAM, T-Mobile is now blocking traffic where the sending Domain is altered from the true sending address: IE, when the domain is actually is senders will receive a 550 bounceback error . To correct this issue, Senders will need to revert their sending address to their actual email address. For assistance, direct customers to the sending party, and sending parties to their domain customer support. this service is functioning properly."

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Thanks for bringing that to my attention. I have resolved the issue with gmail.

Camel is a great tool for sure!

@tmo_amanda and @srickar​ - It looks like @ffit37129​ was able to get this issue fixed for his domain, which is very encouraging!  Who do I need to get in touch with to get the blocking issue resolved for my domain?  Sounds like I need to get whitelisted.  @ffit37129​ - if you can direct message me the info of whoever was finally able to help you, I would be eternally grateful.

Userlevel 3
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Just as an FYI to others, I reviewed the PM you sent and removed the block that was due to high volume. Please check out the PM and let me know if you see messages passing.

I think I did. 


I need help with this issue as well. I think I requested to folllw you.

Userlevel 3
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Hi @isurfer​ - I cant send you a PM until you follow me. When I try to send a message the response is "You can only send messages to your Friends / Connections (people following you)"

Can you follow me back? Ensure its following inbox.

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PM sent with details. For anyone else needing assistance please check the SMTP rejection reason. SPF is one of those external controls that I cannot fix. In @mlauer​ case, it was due to SPF policy rejection.

A major contributor to failing email is SPF policy. Here's my poor analogy and is strictly for amusement: (a reply-to envelope is purely cosmetic and easily tweaked),  but it's actually being sent from say a server located at pretending to be mcdonalds customer service (maybe their next publicity stunt?).

(Sender Policy Framework) is a DNS setting that prevents another ISP or email envelope that doesnt match the SPF DNS record. The error will show like this: "domain of transitioning does not designate as permitted sender)". Since is not in the authorized record, they are not trusted to send email as

Real SPF entry: v=spf1 ~all

In other words, the DNS administrator for needs to edit the DNS record to permit to send emails on their domains behalf. It's a DNS safeguard to prevent someone at say from sending an email that looks like and trying to spoof and represent a domain they don't actually have ownership of.

The domain owner would need to update the SPF DNS record to include any potential IP's or domains that would be sending mail on their behalf.

This is frequently overlooked as businesses experience mergers, buyouts, consolidation, or use 3rd party entities or email services years after their DNS administrator has left the company or forgot about the DNS configuration.

@srickar​ thanks for the information. After investigating is looks like this is actually my issue also and out of your hands. Thanks again!

@srickar​  I am also having the same issue with SMS to Email being blocked by our company's  temperature monitoring service.  I have sent you a follow request.  I need to get our domain whitelisted with T Mobile

We noticed about a month ago we were getting blocked.  I work for the public defenders office and we send court reminders to clients.  Unfortunately we do send a lot out so I could see were our domain could be blocked.  How do I get out domain white listed?

Srickar, I’ve sent a follow request to you. It seems that messages being sent by our companies automated systems are being blocked by T-mobile. We send alarm messages from critical medical equipment and critical research facilities . Our email server is located in Germany ( and hope to get it whitelisted. Thanks in advance.


I am having problems with an email address associated with automation system at work.

Please friend request me

thank you

Hi srickar, I just sent a follow request to hopefully get our SMTP 550 Blocked cleared.I can give you more info in PM. Thanks in advance!

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Please add me to the list of admins with this problem… our email to SMS has been working fine up until the last month with the same error:

Failed to deliver to ''
SMTP module(domain reports:
message text rejected by
550 permanent failure for one or more recipients (,,,


Multiple calls to support have not been fruitful even after pointing them to posts on this forum.


Please give guidance on how to fix this high priority problem.

Please send me a D.M. and I can take a look. Please provide sending domain and at least 1 recipient in the D.M. when you’re ready! Thanks.

Hi, our SMTP line where our message is being blocked: 2019-09-02T01:17:10.118Z,SMTP,08D6F99962F9C532,23,,,<,550 permanent failure for one or more recipients (, can you help us get unblocked? Thanks!