Title: Constant “Authentication Failed” Errors
Last modified: June 22, 2026

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# Constant “Authentication Failed” Errors

 *  Resolved [boardboss](https://wordpress.org/support/users/boardboss/)
 * (@boardboss)
 * [1 week, 6 days ago](https://wordpress.org/support/topic/constant-authentication-failed-errors/)
 * I use Post SMTP on many sites, and I also install the pro version once the free
   plugin is operational. I am using version 3.9.4 of Post SMTP. Unfortunately, 
   I have not been able to successfully send an email from one site.
 * During the setup process, I used the same exact server settings I always use 
   on other sites. I use a password manager, and I copied the username (email address)
   from there, as well as the password, to help avoid typos. Nothing succeeded.
 * I am able to log into the webmail for this email account using the same exact
   credentials. I also deleted the email account in question from my email client,
   and recreated the email account using the same copied-and-pasted credentials.
   No problems.
 * Can you think of anything I might have missed? I am going to raise a ticket with
   my email provider to see if perhaps the server’s IP address might be blocked 
   for some reason, but I cannot think of anything else that could cause this.

Viewing 2 replies - 1 through 2 (of 2 total)

 *  Plugin Support [M Aqib Khan](https://wordpress.org/support/users/aqibkhan9/)
 * (@aqibkhan9)
 * [1 week, 5 days ago](https://wordpress.org/support/topic/constant-authentication-failed-errors/#post-18945668)
 * Hi [@boardboss](https://wordpress.org/support/users/boardboss/),
 * Thank you for reaching out.
 * If you’re seeking support for the Pro version of Post SMTP, I recommend opening
   a ticket through our official website so our team can assist you directly with
   the licensed features.
 * Regarding the authentication issue, if you’re using the Other SMTP socket to 
   send email, I’d suggest testing your configuration with our [SMTP Test Tool](https://postmansmtp.com/smtp-test-tool/).
   It can help identify whether the problem is with your credentials, server settings,
   or connectivity before troubleshooting further.
 * Looking forward to getting this resolved for you.
 *  Thread Starter [boardboss](https://wordpress.org/support/users/boardboss/)
 * (@boardboss)
 * [1 week, 5 days ago](https://wordpress.org/support/topic/constant-authentication-failed-errors/#post-18945911)
 * Thank you for the reply. I am only seeking support for the free plugin. I never
   install the pro version until the free version works.
 * I used the SMTP Test Tool and received the result I expected: the test failed.
 * Since I had tested everything else I could think of, I decided to test the one
   other thing I knew I could control: I changed the password for the email account.
   The test email sent successfully.
 * I use a password manager, so I regularly use long, random passwords, as I do 
   not have to memorize any of them. I am guessing that there must have been some
   pattern of characters that either WordPress or your plugin did not like.
 * Since I am no longer using the old password, I will open a support ticket and
   paste the old password in it so it can be determined what the root cause of the
   issue was. The username/password combination I had worked everywhere but failed
   using the SMTP Post plugin on an up-to-date WordPress site.

Viewing 2 replies - 1 through 2 (of 2 total)

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 * 3 replies
 * 2 participants
 * Last reply from: [boardboss](https://wordpress.org/support/users/boardboss/)
 * Last activity: [1 week, 5 days ago](https://wordpress.org/support/topic/constant-authentication-failed-errors/#post-18945911)
 * Status: resolved