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It's my understanding that besides having another "link in the chain", there's no general reason to avoid using a reliable email relay service. (e.g.: ProofPoint, SendGrid, Mimecast, Postini-RIP etc.)

However, I'm seeking to understand the technical reasoning behind the scenarios in which using an SMTP relay service would create problems, complications or simply not work and thus be undesirable or create an appreciable amount of technical challenges to overcome.

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  • One I can think of: some of these services can have pretty poor spam reputations on some or all of their IP space.
    – ceejayoz
    Jan 18, 2018 at 2:13

1 Answer 1

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ESPs (Email Service Providers) come in a very LARGE range in qualities, as do inbox providers. As with any outsourced service you must rely on the assumption that they will quickly mitigate abuse to their networks, understand the product they are selling (email delivery) and provide you with a better service than you can provide yourself. Since the cost of delivering email is much lower than the cost of delivering physical mail.

A few things you can do.

  1. Ensure the provider offers DMARC Compliant email, (SPF and DKIM)
  2. Require you to provide your own non-purchased list (for newsletters)
  3. Try them out, you can easily send some email via one provider and your in house solution.
  4. Check your own inbox, what providers do the newsletters you see use.
  5. Read the AUP
  6. Request a dedicated IP address (good if you have consistent volume, bad if you don't, helps fight noisey neighbors.

If you have some crappy WordPress on DO, any ESP will be better than trying to setup mail servers in someone else's data center on someone else's IP address. If you have infrastructure, and software that can handle bounces, abuse notifications, delists, blacklists, whitelist, feedback loops... Then do that. Either way it's your domain and your problem :). Self promotion I talk more on this on a podcast linked here

TLDR; In my opinion, no good reason not to use a relay, even if chained with other solutions like data loss prevention or secure email systems (Zix) depending on the sensitivity of the data you send in email.... Don't send sensitive data in email.

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  • Appreciate the response Jacob. I run a small server 'in the cloud' and want to avoid using an SMTP relay because it's an additional expen$e for me. But in order to do that, I need to justify why I can't use an SMTP relay and that's where I'm struggling.
    – JuliusPIV
    Jan 19, 2018 at 13:55
  • You just said it's more expensive, to whom must you justify?? Jan 19, 2018 at 13:57
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    If you need a valid excuse, tell them you have external regulations that require Mutual TLS with partner domains. I'm not aware of a relay that allows this level of configuration. Jan 19, 2018 at 13:59
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    How much do you send, mailgun is 10k/mo for free. Jan 19, 2018 at 14:55
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    First of all, thanks again for the update Jacob - much appreciated. I haven't looked hard (read: at all) so mailgun is new to me and I'll definitely explore that further. I only send maybe 100-150 emails per day. For what it's worth, SendGrid offers two free tiers: 100/day if you sign up via their website and 25k/mo if you sign up through the Azure Marketplace; And Exchange Online Protection is $1/mo/user. The goal here was really just to understand if there were legit reasons why services like that wouldn't work. Again, appreciate the insight and assistance!
    – JuliusPIV
    Jan 21, 2018 at 4:57

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