Install-Module AzureAD Install-Module ExchangeOnlineManagement
Connect-AzureAD Connect-ExchangeOnline
$app = Get-AzureADServicePrincipal -SearchString "IMAP OAuth 2.0" New-ServicePrincipal -AppId $app.AppId -ServiceId $app.ObjectId -DisplayName "IMAP OAuth Service Principal"
Add-MailboxPermission -Identity "MAILTOACCESS" -User $app.ObjectId -AccessRights FullAccess
$startDate = Get-Date $endDate = $startDate.AddYears(99)
New-AzureADApplicationPasswordCredential -ObjectId "OBJECTID" -CustomKeyIdentifier "IMAP Secret" -StartDate $startDate -EndDate $endDate