Hi, Over the past two weeks, I started to notice an increase in the number of S3150 rejections. Example:
550 5.7.1 Unfortunately, messages from [xxx.xxx.xxx.xxx] 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. The main issue is that when I contact them at https://olcsupport.office.com/, I receive a reply indicating that "Nothing was detected to prevent your mail from reaching Outlook.com customers.". I have to reply and wait for them to escalate. After some time, I finally get "We have implemented mitigation for your IP (xxx.xxx.xxx.xxx) and this process may take 24 - 48 hours to replicate completely throughout our system.". Asking for more details about the issue doesn't help as they refuse to provide any. And the main issue is that the IPs will usually get blocked again after a few days. These IPs never had issues before and, after doing a full review, nothing was found on our end. No changes in the content patterns ( mainly invoices and order confirmations ), nothing that indicates that the server was compromised etc. I was wondering if anyone else is also experiencing this type of issue? Thanks.
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