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Why do so many people recommend offloading email to a transactional service such as Mandrill, Postmark or Sendgrid?

Is sending email via smtp really that much slower than sending a request out to said service?

I imagine it has something to do with the rendering of the actual message, but I'd like a more informed reason.

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up vote 7 down vote accepted

I don't think they are suggesting it for speed.

Sending emails becomes a problem when you need to send a lot of them from a single IP. That IP might end up as a spammer and so your emails will not be sent anymore.

Also if you try to send an email and it bounces for some reason, you the sender, must resend it, and check again if it fails and if so, send it again after some more time, and so on.

I think because of this two reasons, people recommend offloading email to some service.

The certainty the mail was sent and received is more important than the speed.

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+1 Sending email to people is not hard. Maintaining the reputation of your email server to other servers can be difficult. – TehShrike Apr 5 '14 at 6:20

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