Sending via SMTP doesn't work, but only in the new Outlook.

Question

Hello everyone, I would like to request some help.

I have a mail server. I tried setting it up via IMAP and SMTP in Outlook with the exact same settings regarding the connection on different devices, different operating systems and different networks. Everything works everywhere, except sending in the new Outlook. I can receive mails, meaning that the IMAP is correct, but even with the exact same settings as everywhere else, the sending part doesn't work, and it only happens in the new Outlook. I always get "550: You are not on the whitelist."

Any help is appreciated.

Answer 1

Hello, thanks for reaching out.

The new Outlook only supports sending through accounts added directly in Outlook. SMTP from external servers may not work if your server blocks unlisted accounts.

You should:

• Add your account using Outlook’s setup (Exchange or Microsoft 365).
• Make sure the server whitelist includes your account.
• Verify your username and password in Outlook match what works elsewhere.