SMTP error in Outlook 0x8004210B

SMTP error in Outlook 0x8004210B

Hello,

We have been having serious problems sending emails though our domain via Outlook in the past few weeks. After about a minute trying to send messages, we get the error 0X8004210B
Our SMTP settings are:
- SMTP server: smtp.zoho.com
- My outgoing server (SMTP) requires authentication enabled
- SMTP port: 587
- Cryptography: TLS

Please, can you help us?