Hello,

We have recently added new ISP and unfortunately, if we try to send an email to any customer who is using Microsoft Online Protection Services the email is bouncing back indicating that our new IP is blacklisted by Microsoft. In order to remove, we have to send an email to delist@messaging.microsoft.com

Is there any telephone number I can reach their support?

Thanks,

I have probably bad news, this e-mail is only valid option to delist currently without direct support contract with Microsoft (when using Office 365 or so).

Sent e-mail to this contact and also check mxtoolbox.com if your ISP is also not blocked somewhere else and why.