Seems eMclient application having Basic authentication (IMAP, POP3). while configuring mail.
Microsoft is going to block basic authentication on tenant wise by sep 2022. So will email work on eMclient after Basic authentication is blocked.
Also does eMclient supports modern authentication?. Please confirm.
Yes, eM Client fully supports Modern Authentication
If your account is setup with a username/password, you will need to remove it and then add it back again using Menu > Accounts > Add Account and the automatic setup.
Note that if the account is setup as POP3, please setup the account using the automatic setup, move the messages from the POP3 folders to the new IMAP folders, then remove the POP3 account.