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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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![Getting Error CNC-SDS-0335 Error returned from SMTP server. The error message was: [535 5.7.8 Error: authentication failed from <IP>]. The message could not be sent.](https://www.ibm.com/support/pages/system/files/support/swg/cogtech.nsf/0/012e928b717190a08525805a00428960/Symptom/0.240.jpg "Getting Error CNC-SDS-0335 Error returned from SMTP server. The error message was: [535 5.7.8 Error: authentication failed from <IP>]. The message could not be sent.")
Getting Error CNC-SDS-0335 Error returned from SMTP server. The error message was: [535 5.7.8 Error: authentication failed from <IP>]. The message could not be sent.
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