[massaman_yams]

The other comments here don't quite tell the whole story; "I never had any problems" is anecdotal - there are plenty of legitimate senders who do run into deliverability issues.

Using an ESP will generally simplify the amount of work necessary to achieve good delivery, but due to the complexities of domain reputation and fingerprinting, very occasionally they can also be the cause of delivery problems.

General guidelines:

- It's a bit harder to predict how deliverability will turn out at smaller ESPs, vs. well-established ones like Sendgrid, SES, Mailgun, and perhaps Mailchimp.

- DKIM, SPF, DMARC (p=none is fine to start; gmail has a guide for deploying dmarc https://support.google.com/a/answer/2466563)

- Use the same root domain everywhere within your email: From, Return-Path, DKIM signature headers; URLs for links and images in the message body. (Separate subdomains are fine, e.g., img.example.com, bounce.example.com)

- Having your sending domain show up in third party email can cause problems. Try to avoid it if possible; use a separate domain as a last resort.

- Send consistently. Some variation in sending patterns will be tolerated, but you'll probably have trouble if you send 500 messages a day most of the time, then once a month you send 100,000 messages.

- Consider a dedicated IP if you're sending over 50,000-ish messages a month.

- You may want to split up transactional email from marketing, sending these from separate IPs and/or subdomains.

- Finally, make sure you're sending email your recipients find valuable and are interested in receiving. Too much disinterest/disengagement can cause delivery issues.

[webbie917]

I agree with all your suggestions, but want to expand on a couple points: 1) The shared IP pool at cheaper providers like Sendgrid, SES, and MailGun will have lower reputation versus a platform with a guarded (via cost, but also on-boarding mechanisms) platforms like MailChimp, simply due to customer pool and quality of emails sent. I have been hearing from my (BigMailer.io) customers about having deliverability issues with platforms like SendInBlue and MailGun frequently in the last year or so. 2) If the bulk sending practices are healthy and engagement is good, then it's better to use the same sender/domain for both bulk and transactional email.

I would recommend to NOT send different email types from different providers, like use SendGrid or SES for transactional emails and then some other platform for marketing emails, especially using the same sender domain. That's because email header signature and tracking links will be different and email box providers like Gmail can find it suspicious and send emails to Spam. And then there is the issue of processing and syncing bounces/unsubscribes/complaints data.

Keeping all email campaign types in a single platform allows for centralized processing of bounces/unsubscribes/complaints date and protects future campaign engagement + sender reputation.

[massaman_yams]

Right. Split up by IP/subdomain if possible, preferably within one provider.

That said, you may be surprised by the number of large organizations that have a dozen or more services that send mail on their behalf, for various different purposes... it's not optimal, from a deliverability perspective, but it's also not usually going to cause deliverability issues by itself as long as everything else is in order.

[webbie917]

Yes, agreed. Lotsa factors in play when it comes to deliverability, like a puzzle. What a well established brand (with high quality emails) can get away with isn't something that businesses with less resources should try to copy though IMO.

Just saw an email from Starbucks in the spam folder - all because of a few words that no doubt triggered the spam filter.