Dreamhost blocking SMTP outgoing email sent via MiFi 4510L hotspot

I've been using a MiFi 4510L as my only internet connection for about a year, and have been happy with it to date.  Dreamhost.com is my email host (and web domain host). 

I haven't been using the MiFi for a few days.  Today I was  unable to send any messages via the MiFi  through Dreamhost's SMTP (outgoing email) server.  This happens both when sending from my laptop's email client (Apple Mail) and also from my iPhone when WiFi (i.e. the Verizon MiFi connection) is enabled.  It's not a mailserver authentication issue -- incoming email works, Dreamhost webmail send and receive  works, and I can send from the (AT&T) iPhone with WiFi turned off (i.e. through AT&T's cellular network).  I contacted Dreamhost support, who said:

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DreamHost now performs spamhaus RBL look ups when using an smtp client such as Apple mail. This is to prevent spam from leaving our network. The issues you are describing is what happens when you attempt to send email from an internet service provider (ISP) that is on the spamhaus blocking list. Switching from wifi to 3g will change that IP address that we look up prior to sending the email. For the device that is blocked we can only recommend that you contact the ISP and ask them to either give you a different IP address or work to get their IP's delisted.

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I take this to mean that Verizon 4G LTE IP addresses have somehow been added to Spamhaus's database.  Has anyone experienced this issue with sending email through a Verizon  device using Dreamhost SMTP?  What are my options?

Message was edited by: John Ciccarelli  (New information: Dreamhost suggested using WhatIsMyIP.com to determine my IP address.  It returned and sure enough Spamhaus has that in its PBL and XBL lists.  However, I'm using Authenticated SMTP (port 587), not the unauthenticated port 25.  Are Verizon servers somehow listed on Spamhaus?)

Message was edited by: John Ciccarelli More research: I repeatedly shut down and powered up the MiFi.  Each time up, WhatIsMyIP.com returns a slightly different IP:,,, etc.  Lookup shows these IPs are associated with vzwdomain.com or myvzw.com, not surprisingly.  So presumably the MiFi gets mapped to a different actual IP each time it connects.  The first of these 3 IPs showed up in Spamhaus's PBL and XBL lists; the other two just in the PBL list.  Perhaps if I keep powering off/on it'll eventually connect via an IP that isn't on Spamhaus's list.