Pantheon Community

Email delivery to Office365 email accounts

I’ve got a client who’s using GoDaddy’s Office 365 email service. We just switched him to Pantheon and have everything working well except for email delivery to him. Emails are being delivered to Gmail-based emails and other services, but stuck on Office 365 accounts. On other sites, we’ve mostly using SMTP Authentication, but this client is hesitant to do that.

What’s been most successful for small site that deliver under 20 emails/day? I’d like to have more confidence in the next step that I recommend to him.


This site is just using the default Pantheon email system to deliver to his O365 account?

As of today, that is correct, just the default Pantheon email system. Obviously, that needs to change – not sure whether to try Sendgrid or other tool, or use SMTP Authentication with an email account that does just this email delivery. Make sense?

I’ve had great luck with Mailgun and outbound email from sites on Pantheon. Been using for 3+ years. Free for the first 10k emails per month. I use with Drupal 7, but I believe it integrates with WordPress too if that’s what you’re using. You would need to create a few DNS records up front as part of the onboarding, but it’s not too bad. I use in Mailgun to avoid any issues with the primary email at

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I imagine SendGrid works just as well and with the same kind of setup. There’s even an official Pantheon guide for them.

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It may be a possibility, at least in the interim, that you could create/modify his SPF record to include whatever the Pantheon outbound email looks like to try to prevent emails from going to his spam.

Thanks for the tip about SPF records. We’re going to try that first.

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Good luck! If you’re using O365 you most likely already have an SPF so should only have to add the pantheon domain to your existing string.

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We use SendGrid and have rarely had a problem. We’ve also never gone over the free tier. For any mass mailouts or EDMs we use Campaign Monitor. It’s worth using a service to increase the chances of actual delivery and to be able to diagnose, a resolve, any issues.

40,000 emails for your first 30 days, then send 100/day, forever $0/mo

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+1 for Mailgun. 10k emails per month vs 100 emails a day from SendGrid. I have used both solutions, both will work on Pantheon and are easy to configure. I prefer Mailgun in case there is ever a spike of emails being sent 10k/mo is a lot more comfortable than 100/day.


I use SendGrid for all wordpress outbound emails. I was going to install the official SendGrid WP plugin, but after reading the reviews it seems to be out of date and not supported very well by SG. Do you use that official plugin or another? I am interested in utilizing the custom categories in SendGrid and don’t want to mess with the API.

We use Drupal with either the SMTP module or more recently Swift Mailer to send email via SMTP. There is a module which uses the SendGrid API called “Sendgrid Integration” but I haven’t used it.

You can add categories by setting X-SMTPAPI headers so any plugin which supports SMTP authentication and adding custom headers should work fine.


Shameless promotion: we’ve had problems with various SMTP related Drupal modules, such as validation issues of correct email address formats and an RFC violation (including within Drupal core). We also needed additional SMTP configuration options.

To this end, PHPMailer SMTP was developed. We’re using it with Sendgrid (but tested with other services) and it’s working very well for our needs.