LADIES AND GENTELMEN
It's a Shared Email Marketing syStem
Constant Contact Wins Stevie(R) Award for Best Customer Service Team in the 6th Annual...
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I was helping a new SPI client today, migrate their email campaigns and email database from Constant Contact to the SPI Email Marketing system.
Constant Contact is a great entry-level "Shared Email Marketing" system.

You can get up and running within a few minutes YOU CAN REGISTE FOR FREE AND YOU GET TWO MOUNTHS FREE AND AFTER YOU BEGIN TO spend a low $15/month for a list size of up to 500 recipients.
Similar solutions include: JangoMail, AWeber, EmailBrain, ActiveTrail and others. All are "Shared Email Marketing" system.
What is a Shared Email Marketing system?
Much like "Shared Hosting" in the web hosting world, a Shared Email Marketing system is running multiple Email Marketing accounts on a single server, sharing the machine resources and in most cases - sharing the outgoing IP Addresses.
Sharing IP Addresses means once a rogue Email Marketing client sends a campaign to a bad list and gets the IP Address black listed, your email deliverability will immediately suffer and you're not even going to know about it.
Email sending rate limits
Due to the nature of how a Shared Email Marketing system works, the Email Service Providers (ESP), fanatically try to protect their limited outgoing IP addresses reputation, by applying rate limits, list size limits, forced list re-validation and restrictions on list acquisition.

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