Sample using EWS

Function Set-TermInboxRule() {

    param(
        [Parameter(Mandatory=$true, Position=0)]
        [Alias('Username')]
        [System.String]
        $userID
    )

    Import-Module -Name "C:\Program Files\Microsoft\Exchange\Web Services\2.0\Microsoft.Exchange.WebServices.dll"

    $user = Get-ADUser -Identity $userID

    #Enter credential to connect to Exchange
    $psCred = Get-Credential
    $cred = New-Object System.Net.NetworkCredential($psCred.UserName.ToString(),$psCred.GetNetworkCredential().password.ToString())

    #Create template email message
    $service = New-Object Microsoft.Exchange.WebServices.Data.ExchangeService
    $service.Credentials = $cred
    $service.AutodiscoverUrl("$($user.UserPrincipalName)",{$true})
    $templateEmail = New-Object Microsoft.Exchange.WebServices.Data.EmailMessage($service)

    $templateEmail.ItemClass = "IPM.Note.Rules.ReplyTemplate.Microsoft"
    $templateEmail.IsAssociated = $true
    $templateEmail.Subject = "$($user.Name) is no longer with <company name>"

    $bodyString = Read-MultiLineInputBoxDialog "Enter the message" "Message" $htmlBodyString
    $bodyString = $bodyString.replace("`n", "<BR>`n")
    $templateEmail.Body = New-Object Microsoft.Exchange.WebServices.Data.MessageBody($bodyString)
    $PidTagReplyTemplateId = New-Object Microsoft.Exchange.WebServices.Data.ExtendedPropertyDefinition(0x65C2, [Microsoft.Exchange.WebServices.Data.MapiPropertyType]::Binary)
    $templateEmail.SetExtendedProperty($PidTagReplyTemplateId, [System.Guid]::NewGuid().ToByteArray())
    $templateEmail.Save([Microsoft.Exchange.WebServices.Data.WellKnownFolderName]::Inbox)

    #Create Inbox Rule
    $inboxRule = New-Object Microsoft.Exchange.WebServices.Data.Rule
    $inboxRule.DisplayName = "Termination Auto Reply"
    $inboxRule.IsEnabled = $true
    $inboxRule.Conditions.SentToOrCcMe = $true
    $inboxRule.Actions.ServerReplyWithMessage = $templateEmail.Id
    $createRule = New-Object Microsoft.Exchange.WebServices.Data.CreateRuleOperation[] 1
    $createRule[0] = $inboxRule
    $service.UpdateInboxRules($createRule,$true)

}