Troubleshoot setting up Microsoft Outlook email

Dear Microsoft Support,

I’m experiencing a critical issue with Outlook for Mac that began a few days ago.

I have two personal email accounts configured in Outlook:

1. A Gmail address — ******@gmail.com — works perfectly in Outlook.
2. A custom domain email — ******@arpartners.ru — suddenly stopped working: it neither sends nor receives emails.

Important details:

• The problem with ******@arpartners.ru began 2–3 days ago without any changes on my side.
• This same email account still works in other mail clients on the same Mac (e.g. Apple Mail).
• I have removed and re-added the account, cleared Outlook caches, reset profiles, reinstalled Outlook — nothing helps.
• No visible error messages are shown — messages simply fail to send or download.

Could you please assist with:

• Troubleshooting why Outlook refuses to send or receive from this custom domain

Thank you in advance for your support.

Best regards,

Karen