[ale] Email to txt.att.net (AT&T Mobile - SMS) being delayed

Wed Jul 1 10:59:43 EDT 2015

As an FYI I was able to rule out issue being RHEL version or Sendmail version.   We can send from other servers using RHEL5, RHEL6 and RHEL7 using either Postfix of Sendmail.   Also as noted initially we can send from Outlook and other Windows servers.

Answer from AT&T is we are being blacklisted due to volume.   They want us to pay for Business SMS. 

My response to that is most (if not all) messages are going to phones we're paying AT&T for as a corporation so we should push back saying we are already paying on the receiving end.   

The interesting thing is that AT&T blacklist appears to be looking not at the server that they got the message from or its IP (our Exchange server) but rather something specific in the header from the Linux server that initiated the email.   This is good because it means our other low volume stuff isn't having the issue so pages for system outages and the like are going out.

-----Original Message-----
From: ale-bounces at ale.org [mailto:ale-bounces at ale.org] On Behalf Of Lightner, Jeff
Sent: Tuesday, June 30, 2015 11:52 AM
To: Atlanta Linux Enthusiasts
Subject: Re: [ale] Email to txt.att.net (AT&T Mobile - SMS) being delayed

Thanks.

I suspect issue is volume based on <user>@<host>.<ourdomain>.com

I may look into procmail.   Currently we use mailer table for sending some email out via a different server.

My next plan is to try adding a *.<ourdomain>.com to DNS to see if maybe they're just rejecting it due to the <host> in the sender name and server name.   (i.e. Maybe they're trying to verify it is a valid host in DNS land.)   I doubt that is the case because I'd think anything checking that would fail on the smtp test I did using shortname vs FQDN.

-----Original Message-----
From: ale-bounces at ale.org [mailto:ale-bounces at ale.org] On Behalf Of Alex Carver
Sent: Monday, June 29, 2015 8:24 PM
To: ale at ale.org
Subject: Re: [ale] Email to txt.att.net (AT&T Mobile - SMS) being delayed

Yes, my carrier is AT&T.

The applications just make a fake From line (no user exists on my system called "cam" for example).  They all send to a real alias on the mail server whose sole purpose is to filter the incoming messages, make copies, and forward them on to the SMS gateway using procmail filtering.

So the mail header is basically:

From: fakedeviceuser at domain.com
To: mycellalias at domain.com
Subject: Message email

And then procmail (on the real user account where the alias points) just
filters:
:0
* ^(From).*mycellalias at domain
{
	#store a copy for archiving
	:0c
	:0
	! phonenumber at txt.att.net
}

After that it arrives on my phone instantly.

However, I do send to other carriers, too, and I see no problems with any of them.  All the SMS messages go through right away, no delays.

I don't know how fast you're sending, that's an important piece of information because I am aware that AT&T does rate limit at times depending on network congestion (especially congestion at the tower servicing the phone).  It's variable, though.  One time I had the system accidentally spew over 100 messages in the span of 3 minutes with no issues.  Other times I had a records of message floods going out that just simply never arrived, only a subset.

In the end I think AT&T is agnostic about where the message comes from when it arrives at the SMS gateway (other than perhaps an RBL) but I have not experienced the problem.

On 2015-06-29 14:11, Lightner, Jeff wrote:
> And is your carrier AT&T?
> 
> Do your applications send as specific users themselves have you done some sort of aliasing or masquerading to make Sendmail do that?
> 
> To be clear I don't believe the issue is an intrinsic fault in the way we're sending email in general.   As noted it works fine to at least 2 other cell phone companies.  I believe the issue is the way AT&T treats the email we send vs the way other carriers do.  My 2 questions were aimed at possible ways to mitigate that based on the findings I provided since they clearly aren't blocking all mail to text messages originating here.
> 
> It is also possible it is a volume thing.   We send many emails so it is possible AT&T is getting the majority of those and is blocking them but if so this is a recent development.    My fear is I'd put in one of the two mitigations I can think of (my original 2 questions) see it resolve the issue temporarily only to recur after AT&T determine the new way of doing it should be blocked.
> 
> 
> 
> -----Original Message-----
> From: ale-bounces at ale.org [mailto:ale-bounces at ale.org] On Behalf Of 
> Alex Carver
> Sent: Monday, June 29, 2015 4:32 PM
> To: ale at ale.org
> Subject: Re: [ale] Email to txt.att.net (AT&T Mobile - SMS) being 
> delayed
> 
> I use the SMS gateway all the time for my alarm system at home (monitored by a Linux machine at home and sending through my personal mail server) and there are no delays.  I can trip an alarm and receive the text message within three seconds using the txt.att.net bridge.
> 
> The from address on those messages is whatever I set in the headers.
> For example, I have one of my Axis cameras sending a message when it detects motion.  It sends by way of my personal server and the message comes out as coming from "cam at acarver.net".  There's a couple scripts running on another machine watching smoke detectors and those relay out through my mail server too.  My relay MTA is exim on the server.
> 
> The current setup has anything that needs to send an alarm send a message to a special alias on my mail server.  That gets sent to my regular user account where procmail picks up the message, duplicates it and ships it off to the SMS gateway.  The response is immediate and the text message arrives at my phone the moment it leaves my server.
> 
> One thing I used to have in place was a MIME decoder because the message would be a mess of MIME and text.  I'm not using that currently, though.
> 
> 
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