E-mail service providers are companies like Constant Contact and Vertical Response that track and manage legitimate bulk e-mailing.

So what do e-mail service providers have to offer?

Improved Deliverability

The best e-mail service providers maintain their own anti-spam protections so that they can pass the high quality e-mail reputation along to their customers.   Because emails made through an ESP call upon its email reputation (and not your own), by using an ESP you will be able to move mass mailings past most ISP level spam filters even when you are using a brand new account.

Moreover, email service providers are set up to track which of your e-mails are delivered, and when they aren’t they will use their ties with the various internet service providers to determine and work through any issues, thereby ensuring higher deliverability.

Legal Compliance

Even if you are unfamiliar with the ins and outs of the CAN-SPAM law (and other spam e-mail legislation) e-mail service providers are, and they ensure that their subscribers are in compliance.  This is why you will find an unsubscribe link at the bottom of every Constant Contact e-mail you ever receive.

Mailing List Management

Because e-mail list maintenance is an integral part of e-mail compliance, most email service providers will also help you manage your online mailing lists, and may even make tools available to you to help you legitimately gather email addresses.

Superior Formatting

Email service providers use a multi-part email format that ensures recipients will always receive the email in the best format for their email client.  Most e-mail clients will only produce a plain text email or an HTML email.  This is important because HTML e-mails look like gibberish when received by applications that can’t read HTML, while plain text e-mails get ¼ fewer responses when viewed on applications that can read HTML.