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Failed to authenticate on SMTP server with username


Error “Failed to authenticate on SMTP server with username” – Causes & fixes

Almost every PHP application relies on mail functions to send contact requests, newsletters, and more.

The most secure way to send these mails is to use SMTP authentication – that is, the PHP app uses a username and password to transfer mails to an SMTP server.

But this authentication can sometimes fail with the error:

Failed to authenticate on SMTP server with username "user@example.com" using XX possible authenticators

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