Outlook Error 421 - Version 3.2 There is an important announcement to all Outlook users. If you are worried about your Outlook error 421 then your worry is not worthless. There are various reasons of corruption of Outlook data. No need to worry. "An unknown error has occurred. Subject 'Testing', Account: 'pop.charter.net', Server: 'mail.charter.net', Protocol: SMTP, Server Response: '421 Message rejected', Port: 25, Secure (SSL): No, Server Error: 421, Error Number: 0x800CCC67”Various reasons of Outlook error 421 are: more than 2GB PST files, virus, or Trojan attack, corrupted or PST file, incorrect ISP settings, etc. Our Outlook email recovery tool is the most beneficial tool in the case of Outlook PST files corruption. Let's have a look on all the qualities of the software:• Recover password protected emails• Recover PST files even after the bytes deletion• Recover all the broken PST files• Manage all the Outlook mailbox items• Get access Outlook emails