Thanks for the suggestion. We are not running any kind of fail2ban type filter.
Packet capture FTW. It turns out the error message wording is misleading and there is some kind of either router filter or an actual routing issue somewhere on or between Cogent and Verizon networks, in or around Minnesota, best I can tell at this time. My SMTP server's SYN-ACK packets appear not to be reaching the initiating IP address so we keep retransmitting SYN-ACK while they keep sending SYN packets. I adjusted some BGP knobs (local pref) on my side to avoid the problem area and traffic is passing fine now between my SMTP servers and the Verizon ones. As we are not a Verizon customer I have limited visibility with them but anyone can reproduce the behavior using Cogent's looking glass server alone. Test from Cogent's Minneapolis router and the traffic dies early at Verizon (ping and trace). Test from Cogent's Denver router and the traffic reaches the Verizon destination server. I did open a ticket with Cogent. But for now, email mystery solved and network mystery activated. -----Original Message----- From: Michael Orlitzky via mailop <mailop@mailop.org<mailto:michael%20orlitzky%20via%20mailop%20%3cmai...@mailop.org%3e>> Reply-To: Michael Orlitzky <mich...@orlitzky.com<mailto:michael%20orlitzky%20%3cmich...@orlitzky.com%3e>> To: mailop@mailop.org<mailto:mailop@mailop.org> Subject: Re: [mailop] Verizon text to email on vtext.com - connection refused error Date: Tue, 02 Jan 2024 12:45:47 -0500 On Tue, 2024-01-02 at 17:32 +0000, Justin Krejci via mailop wrote: When a Verizon mobile user sends a text to an email recipient, I understand it goes through some mail gateway system that converts the message to a standard email and I think uses the @vtext.com as the sending domain with some composition of obfuscated user data before the domain. We are receiving many reports of people getting "connection refused" errors when a Verizon user is sending with this method; see below for error message. Is there anyone on the Verizon mail admin team we discuss/troubleshoot with please? Our receiving SMTP server is definitely not refusing connections so either tcp traffic is getting blocked before arriving to us or the wording of the error message is not accurate. But without knowing what all the sending IP addresses are for sure, it is difficult to even troubleshoot. We are attempting to run a packet capture on the IP addresses listed in the SPF record for vtext.com but that uses assumptions which may be incorrect. Wild guess: a few weeks ago we were getting reports of missing SMS-to- email messages because the Verizon servers involved were blacklisted. If you have something like fail2ban running, maybe you're dropping them at the firewall for some kind of abuse? _______________________________________________ mailop mailing list mailop@mailop.org<mailto:mailop@mailop.org> https://list.mailop.org/listinfo/mailop
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