When using a managed dedicated IP pool for mailings, the emails using Microsoft domains (Hotmail, Live, MSN, Outlook, etc) are soft bounced with the following error message:
Action: failed
Final-Recipient: rfc822; xyz@hotmail.com
Diagnostic-Code: smtp; 550 5.7.1 Unfortunately, messages from [54.240.53.199] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3150). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. [BN8NAM11FT015.eop-nam11.prod.protection.outlook.com 2023-07-17T15:04:32.309Z 08DB86C8320E9038]
Status: 5.7.1
Apparently the IP address 54.240.53.199 that was assigned automatically to our managed dedicated IP pool is blocked somewhere.
According to https://multirbl.valli.org/lookup/54.240.53.199.html the IP address is currently on 9 public blocklists.
My questions:
- why are IP-addresses used that are on (public) blocklists? We choose using paid managed dedicated IP pools to prevent exactly this...
- we sent one mailing at 17:00, resulting in hundreds of soft bounces in a few minutes by an "important" party like Microsoft due to use of a blocklisted IP. One hour later at 18:00 we sent another mailing which also resulted in hundreds of bounces since the same IP was used. How "managed" is this IP-pool? How do these bounces affect the used IP addresses? Isn't there some kind of mechanism that rotates the IP address when hundreds of bounces occur within minutes?
- what to do in such case? Open a support case (I did, they referred my to asking the question here...)