At a previous company I worked at we used to manage our own email infrastructure before finally switching over to a dedicated service. There are a few problems if you are sending over bulk email that is customized per user when running your own SMTP service.

1. IP address reputation - Keeping your IP addresses reputable is not a simple task. It requires balancing your emails for popular destination domains (gmail.com, aol.com, yahoo.com, etc.) across multiple external IP address. It requires you to deal with many different conflict resolution departments, who don't care about email, when a dispute comes up. It's practically a requirement to use a service like ReturnPath to maintain your reputation.

2. Throttling - When doing it yourself you need to throttle yourself. This is problematic on "big" days, especially when your marketing department wants to send many millions of emails for a big product push, promotion, or on days like black friday/cyber monday.

3. Hiring - A lot of people think sending email is easy. When you get up to the multiple million per day mark things start to fall apart. Do you have someone(s) on staff who really know sendmail/postfix/qmail inside and out?

4. Monitoring - sendmail/postfix/qmail are often times hard to monitor. You have to put together all of your stats. You have to put together all of your alerts. If you aren't really experienced with bulk email, you won't know what to look for and that can impact your reputation. Also consider your logging infrastructure. sendmail/postfix/qmail are noisy.

5. Cost - All of the points above play into the cost aspect of it. Is it cheaper to run it yourself, pay for all of the services and salaries, etc. Or is it actually cheaper to just use sendgrid/mailgun/etc. IP address reputation services are not cheap. Infrastructure cost is also something to consider. AWS IPs all have pretty terrible reputations so running this in AWS (and maybe other cloud providers) is a non-starter since no one will accept your email.

If you've got the expertise and you are sending a massive amount of emails then it might be worth it to run your own infrastructure, but at the end of the day, a single developer consuming an API is often easier and less problematic.

The other important one, at least in the US, is unsubscribe/CAN-SPAM compliance [0]. You've got 10 days to comply or you'll be at risk of up to a $41k fine per email!

[0] https://www.ftc.gov/tips-advice/business-center/guidance/can...

My favorite features:

1. SAAS web app to manage the service with logs, and configuration as well as multi-user management with various roles. 2. HTTP Rest-like api for sending mail from your app 3. API keys for authentication, managed through web app 4. They do monitor black-lists and removals from blacklists. They also manage the warm-up time for your IP to make sure it is ready to send the volume of email you are sending, and can queue emails to avoid sending too many at once to the same destination mail service. 5. Spam control, in case you use the key in an app that turns out to have a relay vulnerability. 6. Return-path management to catch blocks and smtp errors.

I've managed my own SMTP services with PostFix and SendMail, and I will never go back to doing that myself again. It would take a lot more than 1M emails/month to make that worthwhile.

The API alone is pretty amazing. SendGrid allows you to send up to 1000 customized non-campaign (transactional) emails in a single call. This is huge if you send a ton of email. Plus the deliverablity stats for transaction emails is great, too.

Sending a high volume of mail through a server with a new IP will raise red flags.

If cost is a concern it does pay dividends in the long run though. Biggest hassle is the initial setup.

It warrants physical infrastructure, which for many companies this is a non starter. Cloud IP addresses tend to have pretty terrible reputations with email clients.

Generally if you run your own server at any reasonable volume, you will be blocked by anti-spam algorithms and once your domain makes a blacklist, it's very difficult to get it reinstated.

You can't know if your IP is already tainted until you realize your mails are landing in people's spam box.

I use one of the service even for my private email server (which is essentially free for the volume being sent), so I don't have to have stupid conversation like check for spam box whenever I send emails.

Having emails land in spam box pretty much makes your email non existent with the volume of spams being sent today. What is the reason not to use one of the services either privately or professionally?

> Is there some back magic that these services perform to avoid getting blacklisted?

Yes. No matter what your project is, unless your secret sauce has to do with email delivery or your business model requires email delivery to be free, do not attempt to roll your own email delivery service. No one has ever looked back and wished they had.

What is the missing sauce? My understanding is that once your sending IP has some history and has developed a reputation as not sending spam, there isn't anything offered by Sendgrid that improves upon that.

If you set up SPF and Domainkeys/DKIM that is an added vote of confidence but Sendgrid doesn't even require it, so I think most of the value of Sendgrid is simply offering a stable IP address and a convenient API. Am I wrong?

Read here: https://news.ycombinator.com/item?id=18225068

That poster gave a very detailed breakdown, but point #1 is enough to make anyone who’s done this before cry in a corner from the abuse they endured.

If you go this route, I would recommend a separate domain for any emails that are are bulk in nature.

Keep the one off transactional ones on a different domain. Then, if your bulk emails cause a false positive, you haven't burned essential things like receipts, password resets, shipping notices, etc.