For this, you can:  Make sure that your internet connection is working well  Verification of Outlook email account settings  To review firewall settings and disable email scanning with the help of an Anti-Virus program  To repair your Outlook or Outlook Express  Run the Inbox Repair Tool to repair yours. PST file  To Try an Outlook repair tool to fix a corrupted PST/OST file  To Delete Suspected Message from Mailbox  To make sure that your email profile works properly  To restart Outlook in safe mode  To Delete Messages that are stuck in Outbox  To Run MAPI Repair Tool  Presence of the Incorrect Mail Address in SMTP Distribution List