How to fix [Message=421 4.3.2 Service not available] error? Post author:Amit Singh Post published:August 22, 2022 Post category:Microsoft 365 Post comments:0 Comments Recently we have faced an issue in Office 365 test account where we cannot send email from our Office 365 test account to our On-Premises Exchange Server. Note: Our On-Premises Exchange… Continue ReadingHow to fix [Message=421 4.3.2 Service not available] error?