What cloud email delivery services are larger companies using? [on hold]

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http://serverfault.com – Some background: a client of mine is using Mailchimp to distribute paid subscription-based emails 3-5 times per week to a few thousand email addresses. They are encountering deliverability issues because the vast majority of subscribers are at large companies with stringent IT departments, and the email content is essentially a digest on the pharmaceutical industry (obesity/weight loss drugs, earnings reports, lots of references to drug names, etc). It isn't really an option to change the content of the email because, well, that's what the subscribers are paying to read about. A recurring iss (HowTos)