We love SendGrid
For those who do not know whom SendGrid is / we use them to send out all email transactions from our billing hosting apps / we run a couple of WHMCS ....
SendGrid is a fantastic SMTP outbound mail service that also will allow you to track receipt and when the end user opens the email ( has to be html ) but that in of it self is great for those clients that are late in payment and claim they never got the email and such.
Provides great reporting tools and stats on email sends and such.
But check it out / we have no connection to them http://www.SendGrid.com
Sign up for a free account up to 200 emails per day : https://sendgrid.com/user/signup
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