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![authentication failure [SMTP: STARTTLS failed (code: 220, response: 2.0.0 SMTP server ready)] · Issue #5392 · osTicket/osTicket · GitHub](https://user-images.githubusercontent.com/36020960/75769500-4abd6a00-5d6c-11ea-8963-6500bbc5c7b3.png "authentication failure [SMTP: STARTTLS failed (code: 220, response: 2.0.0 SMTP server ready)] · Issue #5392 · osTicket/osTicket · GitHub")
authentication failure [SMTP: STARTTLS failed (code: 220, response: 2.0.0 SMTP server ready)] · Issue #5392 · osTicket/osTicket · GitHub
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![Resolved] 421 Cannot Connect to SMTP Server Error in Outlook](https://www.partitionwizard.com/images/uploads/articles/2021/05/421-cannot-connect-to-smt/421-cannot-connect-to-smt-thumbnail.jpg "Resolved] 421 Cannot Connect to SMTP Server Error in Outlook")
Resolved] 421 Cannot Connect to SMTP Server Error in Outlook
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6 Ways to Solve Outlook Error “421 Cannot connect to SMTP server”
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SQL SERVER - Database Mail Error: The SMTP Server Requires a Secure Connection or the Client was not Authenticated. The Server Response Was: 5.5.1 - SQL Authority with Pinal Dave
FIX: Error 421 cannot connect to SMTP server in Outlook
