Hi, I hope someone can help with this. All of a sudden I can't send to Hotmail addresses - was working fine up until yesterday. Here's the full message that I get: The following message to <[email protected]> was undeliverable. The reason for the problem: 5.1.0 - Unknown address error 550-"5.7.1 Unfortunately, messages from [134.153.136.23] 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. [DB3EUR04FT045.eop-eur04.prod.protection.outlook.com]" Reporting-MTA: dns; esa03.ucs.mun.ca Final-Recipient: rfc822;[email protected] Action: failed Status: 5.0.0 (permanent failure) Remote-MTA: dns; [104.47.12.33] Diagnostic-Code: smtp; 5.1.0 - Unknown address error 550-"5.7.1 Unfortunately, messages from [134.153.136.23] 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. [DB3EUR04FT045.eop-eur04.prod.protection.outlook.com]" (delivery attempts: 0) Any thoughts or help is much appreciated. Got the same result with another friend who has a Hotmail account. Thanks! Thanks Adrian