Having emails stuck in the inbox is a fairly common problem in Gmail: the user wrote an email, clicked to send it, but stays in the inbox folder and Gmail doesn't send the email, no matter what. This article details the possible causes and solutions and applies to Gmail or Google account. There may be many reasons why Gmail would not send an email. To reduce the cause of the emails stuck in the inbox, the user must first verify if he receives an error message while performing a Send / Receive operation.
If Gmail user receives an error message when trying to send the email
Most likely, there is a communication problem between Gmail and the users' outgoing mail server, so the email is stuck in the inbox because Gmail can’t connect to the users' mail server to send it.
The problem is likely to be related to the local Gmail settings of the users. If Gmail does not send only some emails in the inbox, make sure that the user does not have the habit of previewing / opening / clicking the emails in the inbox: the emails in the inbox User input should not be read (marked with bold and italic) otherwise, Gmail will. Do not send the email and it will get stuck in the user's inbox folder. Verify user emails:
If Gmail does not send any of the users emails in the inbox and they are not marked as read (as indicated above) try one of the following solutions: Make sure that Gmail is not set to offline mode. The user can check if Gmail is disconnected from the Send / Receive ribbon button (toolbar): Make sure that the user does not have an antivirus that is too enthusiastic to scan emails in the inbox of users and prevent them from being sent. Make a simple test and disable the antivirus protection of users, restart Gmail, and try to send emails from the inbox once again. If they are sent, configure antivirus users and prevent them from scanning emails in the inbox.