In the Send/Receive section, enable Send immediately when connected.In the Options dialog box, select the Mail Setup tab.In the Send and receive section, enable Send immediately when connected.In the Outlook Options dialog box, select Advanced.Use the following steps to re-enable the Send immediately when connected option. In the above registry key paths, represents the Outlook version (16.0 = Outlook 2016, Outlook 2019, or Outlook for Office 365, 15.0 = Outlook 2013, 14.0 = Outlook 2010, 12.0 = Outlook 2007, 11.0 = Outlook 2003). Policy key: HKEY_CURRENT_USERSoftwarePoliciesMicrosoftOfficeOutlookOptionsMail Key: HKEY_CURRENT_USERSoftwareMicrosoftOfficeOutlookOptionsMail
This setting is tied to the following registry data, so this setting can also be configured by an administrator through a modification of the registry. This problem can occur if the Send immediately when connected option is not enabled, as shown in the following figure from Outlook 2016. When this problem occurs, the message remains in your Outbox folder until you manually initiate a Send/Receive operation (for example, press F9 or select send or receive). When you send an e-mail message in Microsoft Outlook, the message may remain in your Outbox folder as shown in the following figure.
