Google announced that from May 30, 2022, Google no longer supports the use of third-party apps or devices which ask you to sign in to your Google Account using only your username and password.

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Less secure apps & your Google Account - Google Account Help

Because of it, the sending error is occurred if i-PRO products send e-mail by using Gmail with the user name and password for Gmail.
To continue using Gmail use App Password instead of user name and password for Gmail.
An App password is a 16-digit passcode that gives a non-Google app or device permission to access your Google Account.
Also see below for more information.
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Sign in with app passwords - Google Account Help