I’ve been using the Mailgun service to send automated emails to my users. When I check the Mailgun dashboard, it shows successful delivery to all email providers. However, I’m having a strange issue specifically with Outlook accounts.
Emails reach Gmail and Yahoo accounts without any problems. But when sending to Outlook or Hotmail addresses, the emails seem to disappear completely. I’ve already checked spam folders and junk mail sections but found nothing.
The weird part is that Mailgun logs show successful delivery status like this:
Since the logs indicate delivery success, I’m confused about where these emails are going. Has anyone experienced similar issues with Outlook email delivery through Mailgun? Any suggestions would be helpful.
I encountered this exact problem about six months ago with my client notification system. The issue turned out to be related to Microsoft’s spam filtering being more aggressive than their interface suggests. Even though you checked the spam folders, Outlook sometimes quarantines emails at the server level before they even reach the user’s mailbox. What solved it for me was implementing proper SPF and DKIM records in my domain DNS settings, plus adding a custom tracking domain in Mailgun instead of using their default sandbox domain. Microsoft’s filters seem to scrutinize emails from shared sending domains more heavily. After making these changes, my delivery rates to Outlook addresses improved dramatically. You might also want to check if your sending IP has any reputation issues with Microsoft specifically, as they maintain separate blacklists from other providers.
outlook has this annoying thing where they dont always show bounces or rejections properly. try whitelisting your sending domain directly with microsoft - sometimes their algorithms flag legitimate transactional emails as bulk mail even when authentication is perfect. also check if youre hitting any rate limits, outlook can be picky about that stuff compared to gmail.
Check Microsoft’s postmaster tools at postmaster.live.com to see if there are any delivery issues specific to your domain or IP address. I had a similar situation where Mailgun reported successful delivery but emails weren’t reaching Outlook users. The problem was that Microsoft was silently dropping emails due to content filtering rules that were stricter than what showed up in spam folders. In my case, certain phrases in the subject line were triggering their filters. I also discovered that using sandbox domains with Mailgun can hurt deliverability with Microsoft services. Try sending a test email with very basic content and a simple subject line to see if it gets through. If basic emails work but your regular ones don’t, then it’s likely a content filtering issue rather than authentication problems.