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.