Enable and configure IMAP4 on an Exchange server … POP3 and IMAP4 functionality in Exchange 2016
Start the IMAP Services and to Automatic.
Using PowerShell –
Start-Service MSExchangeIMAP4; Start-Service MSExchangeIMAP4BE
Set-Service MSExchangeIMAP4 -StartupType Automatic; Set-Service MSExchangeIMAP4BE -StartupType Automatic
Using GUI –
open Services.msc – Set IMAP to automatic and start it
To be Run on all Mailbox Servers
Set-ImapSettings -ExternalConnectionSettings "mail.azure365pro.com:993:SSL","mail.azure365pro.com:143:TLS" -X509CertificateName mail.azure365pro.com
Test-ImapConnectivity –ClientAccessServer Servername -Lightmode -MailboxCredential (Get-Credential)
Also Run
Restart Pop and IMAP services to Take effect.
Restart-Service MSExchangeIMAP4; Restart-Service MSExchangeIMAP4BE
Outlook 2016 Client Settings for IMAP to work.