Hi Jim,
I do a lot of work with email lists with my marketing department at work and work with email hosting with some customers that have similar problems from time to time.
If your not already doing it, It's best practice to break your marketing lists up to smaller batches several hours apart with such large numbers, or spam filters can automatically get your IPs blocked because it can come across as a spam attack when hundreds of thousands of email go out at once.
Spam filters now track senders reputation by sending domain, and /or by DKIM identity, and virtually all blacklists now share reputation information among themselves in near real-time.
You also don’t have to be a spammer to get reported for spamming.
Clean lists that are 100-percent double opt-in will normally get one or two abuse reports per 50,000 recipients. Sometimes it’s a simple user mistake when a user cleans their spam folder, any email that was in the spam folder can be recorded as spam by Microsoft and they have to act.
But even if it’s a mistake, getting reported for abuse is serious. If a major ISP receives even a small handful of complaints about your emails, then they’ll start blocking all email from your server.
Also do you send your own email or use a service? Maybe the service provider has been blacklisted, its not uncommon for them to get hijacked or abused occasionally and effect real paying customers. Your JRiver.com domain isn't blacklisted anywhere that I can find.
You do have a problem somewhere though.
FAIL
Acceptance of postmaster Mailserver rejected mail to postmaster. Mailservers are required by RFC822 6.3, RFC1123 5.2.7, and RFC2821 4.5.1 to have a valid postmaster address that is accepting mail. The Mailserver provided is:
216.14.187.176 | unexpected response to [RCPT TO: ] | 450 Rcpt to - Temporary local problem - I said try later
FAIL
Acceptance of abuse Mailserver rejected mail to abuse. Mailservers are required by RFC2142 Section 2 to have a valid abuse address that is accepting mail.
216.14.187.176 | unexpected response to [RCPT TO: ] | 450 Rcpt to - Temporary local problem - I said try later
WARN
SMTP greeting Malformed greeting or no A records found matching banner text for following servers, and banner is not an address literal. RFC5321 requires one or the other (should not be a CNAME). If this is not set correctly, some mail platforms will reject or delay mail from you, and can cause hard to diagnose issues with deliverability. Mailserver details:
216.14.187.176 | WARNING: The hostname in the SMTP greeting does not match the reverse DNS (PTR) record for your mail server. This probably won't cause any harm, but may be a technical violation of RFC5321