If you’re unable to send emails to specific addresses, the issue may not be caused by your Office 365 account settings, but rather by interoperability between different email service providers.

🧭 Recommended Steps

1. Contact the destination provider
   • Inform them that emails from your address are not being received
   • Ask if there are any blocks, filters, or delivery restrictions in place
2. Contact your source provider (e.g., IIJ)
   • Report that emails to the destination address are not being delivered
   • Request a review of outbound mail logs or any delivery errors

📌 Important Notes

• The Office 365 Help Desk supports issues related to Office 365 functionality, but does not troubleshoot delivery issues between external email services.
• Email delivery problems may involve:
  • DNS or SPF record mismatches
  • Blacklisting or spam filtering
  • Server-level blocks or throttling