If you're using it for outbound mail, you might look at using Mandrill. They're much bigger -- it's MailChimp's backend, used by 5M companies. That means mail is their primary business, their ISP relationships are solid and you can count on them to have 24/7 staff if anything does go wrong. They're also quite competitive: 12K free e-mails per month, then cheaper than both Mailgun and Sendgrid.
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If you're using it for outbound mail, you might look at using Mandrill. They're much bigger -- it's MailChimp's backend, used by 5M companies. That means mail is their primary business, their ISP relationships are solid and you can count on them to have 24/7 staff if anything does go wrong. They're also quite competitive: 12K free e-mails per month, then cheaper than both Mailgun and Sendgrid.
http://www.mandrill.com/