### Generate a new Certificate, replace the DomainName with your Exchange Domain
New-ExchangeCertificate -KeySize 2048 -PrivateKeyExportable $true -SubjectName "cn=Microsoft Exchange Server Auth Certificate" -FriendlyName "Microsoft Exchange Server Auth Certificate" -DomainName "exchange.domain.com"

### Set the new generated Exchange Certificate as Authentication Certificate
Set-AuthConfig -NewCertificateThumbprint <ThumbprintFromStep1> -NewCertificateEffectiveDate (Get-Date)
Set-AuthConfig -PublishCertificate
Set-AuthConfig -ClearPreviousCertificate

### Restart the IIS Server (needs Administrator Privileges)
iisreset /restart