Mail php code Fix --SMM Tools Pro

We are having an error on our website which emails documents to users after completion of creating the document. The problem should be relatively simple and should have to do with a gmail password issue (not complicated), but we have not been able to resolve. We are getting the following error message below. We operate a wordpress site and use cpanel to host it. Applicants should understand php, wordpress and understand how to navigate around a cms generally. Cpanel experience preferable. We need this done as soon as possible. This has happened once before and I recall it was a very simple, quick resolution. [login to view URL] SMTP -> ERROR: Password not accepted from server: 535-5.7.8 Username and Password not accepted. Learn more at 535 5.7.8 [login to view URL] d65sm7733920oih.1 - gsmtp SMTP Error: Could not authenticate. Mailer error: SMTP Error: Could not authenticate.