Unusual Email sending issue
Hi, Thunderbird is doing something very unusual. -I send and receive emails to and from everyone but 1 specific email address. -When I email that specific email address but directly from web mail (same account), they get it with no issues. -When I do it with Thunderbird I get this error: wfs-aero.mail.protection.outlook.com (104.47.5.36) reason: 550 5.7.1 Service unavailable, Client host [74.208.4.194] blocked using Customer Block list AS(1420) [HE1EUR02FT023.eop-EUR02.prod.protection.outlook.com] -Everything pointed to a block list, but they receive from my email when web mailing. -Now the weird part..when I send with Thunderbird to that specific email and I "CC" someone else the email gets through to the recipient with no issue. Any help? Thanks!
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It's not Thunderbird's doing. The non-delivery report (NDR) indicates the client host is indeed blocked. A search of that IP address in the abuseipdb site reveals this:
This IP address has been reported a total of 129 times from 104 distinct sources. was first reported on May 23rd 2018, and the most recent report was 1 day ago
and a further warning saying:
Recent Reports: We have received reports of abusive activity from this IP address within the last week. It is potentially still actively engaged in abusive activities.
This is not something you can fix on your end as the sender. Also note that there are differences between sending mail via webmail, and using a client and smtp server like Tbird. One method may fail and the other succeeds for various reasons. Check your private messaging inbox for a link to information that you can share with the recipient, who should in turn engage their IT personnel or admin to get it resolved on their MS 365 account configuration or to have that blocked IP delisted. 1&1 IONOS, to whom that blocked IP is allocated, should also be engaged so that they can look into those abuse reports and act accordingly.