Procedure
1. Start Outlook 2021 and choose File > Info > Add Account. 
2. Input your email address, select "Let me set up my account manually" and click "connect".
3. Select POP3 or IMAP option. Here we use IMAP settings as example.
4. Input the password of your account and click "connect".
5. Fill the "IMAP Account Settings" and click "Next" to finish configuration.
The server addresses are as follows.
Protocol | Mail server | Port number (normal) | Port number (encrypted) |
POP3 | pop.sg.aliyun.com | 110 | 995 |
IMAP | imap.sg.aliyun.com | 143 | 993 |
SMTP | smtp.sg.aliyun.com | 25 | 465 |
We recommend that you use SSL encrypted connections which are more secure. Please ensure that encrypted ports 465, 995 and 993 are open on your local machine and network first.
6. If the credentials you filled are correct, it will inform you that account is successfully added. Now you can use Outlook to send and receive emails.