Do tele2.nl operate a email blacklist/blocklist? I am trying to send a friend who has a tele2.nl email account an email via Campaign Monitor (a large, well known mailing list company).
Multiple emails, over many months, have been rejected with the following message:
smtp;550 Sorry, we do not accept connections from you
The from address and return-path domains are cmail1.com through cmail20.com and the full allow list of domains and IP addresses at https://help.campaignmonitor.com/whitelist-campaign-monitors-addresses
I am wondering whether tele2 has mistakeningly added them to a block list?