I manage an email server that uses an Atlantic Broadband SMTP server as a smart host. I maintain a mailing list on the server that currently has about 1,300 email addresses. Each month someone sends a monthly newsletter to the email addresses in that list; the people associated with those addresses are all members of a retirees organization and have all indicated they wish to receive that organization's newsletter. Usually, the newsletter is transmitted without problems, but occasionally I will find that email transmitted from the server is silently discarded with no bounced emai indicating why that is occurring. Though that doesn't occur often, when it occurs, it usually occurs when the newsletter is sent. When the problem occurs, as it did yesterday, I have to request that the IP address of my server be unblocked. Initially, I would call the ISP's phone support number, i.e, an Atlantic Broadband support number, but they would in turn have to contact their email service provider, since the email service they provide is outsourced to Echo Labs as I found from examining email headers - see Email sent via an Atlantic Broadband SMTP server not being delivered. But I found that I could get the block removed more quickly if I submitted a request through Cloudmark, an anti-spam company co-founded by Vipul Ved Prakash and Napster's co-founder Jordan Ritter, which provides an anti-spam service used by Echo Labs.
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