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Old 21 Aug 2018, 02:43 AM   #1
Junior Member
Join Date: Aug 2018
Posts: 2
Would an ISP block outgoing email to a certain domain or IP?

I am a hosting reseller and one of my clients has a chronic problem. They never get emails from a handful of specific email accounts they deal regularly with. They have to ask those specific contacts to send to an alternate email account (different domain, but another one I host on the same server) instead of their regular business account. I have whitelisted the incoming email accounts in SpamAssassin - and even turned it off completely, but it made no difference. No failure notifications bounce back to the sender. When I asked the hosting company through which I am a reseller what might cause this, they suggested the various senders' ISPs might be blocking outgoing mail to this specific domain. To me, that sounds very implausible because it's an odd coincidence that maybe five different domains are having this problem. The common denominator is us, not them. Secondly, why would an ISP target outgoing mail to a specific domain - incoming makes sense, but outgoing? Is there a reason for this I haven't thought of? This has been an unsolved issue for months and I'm getting nowhere dealing with my hosting company.
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Old 21 Aug 2018, 01:39 PM   #2
Intergalactic Postmaster
Join Date: May 2004
Location: Irving, Texas
Posts: 8,476
Arrow Transport Layer Security test or outgoing IP/server block

I suggest checking the domains which are having difficulty against the new EFF Transport Layer Security website:

If those domains donít allow properly secured incoming connections, some outgoing SMTP servers might not allow a connection to send mail, since the transfer could be compromised.

Outgoing email servers may block connections to IP addresses or servers which are thought to be insecure. This is to prevent malware or bad links in email messages connecting to spammer servers. So be sure that the IP ranges are not on any block lists.

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Old 21 Aug 2018, 06:42 PM   #3
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Location: USA
Posts: 1,336
I wonder if thats why doesnt seem to send to ALOT OF DOMAINS!! (Or if they have it locked down to try and combat spam being sent)
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Old 22 Aug 2018, 01:29 AM   #4
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Join Date: Aug 2018
Posts: 2
I'm not sure what to make of the results. I tested my client's domain ( at and I get the following, each and every time and also whenever I test my other clients on the same server:

Something went wrong
There was an error processing your request to scan Please try again later.

I went to and ran their test (of the receiver as opposed to the sender) and everything looks fine. I had trouble testing the sender from my own domain (on the same server) because I never get a response back from them at, even though I whitelisted their domain, as per their instructions. My domain doesn't show up in their error logs either.

It seems like something is not right, but 'There was an error processing your request' doesn't tell me much about what happened.

I also tested two mail accounts whose emails never get through to One passed the test and one failed.

Any ideas? I'm not sure I know how to interpret all of this.

Thanks for the replies.
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