Note In the above registry key paths, x.0 represents the Outlook version (16.0 = Outlook 2016, 15.0 = Outlook 2013, 14.0 = Outlook 2010, 12.0 = Outlook 2007, 11.0 = Outlook 2003).
Please use the following steps to re-enable the Send immediately when connected option.
Outlook 2010 and later verisons
On the File tab, click Options.
In the Outlook Options dialog box, click Advanced.
In the Send and receive section, click to enable Send immediately when connected.
Outlook 2007 and Outlook 2003
On the Tools menu, click Options.
In the Options dialog box, select the Mail Setup tab.
In the Send/Receive section, click to enable Send immediately when connected.
Note: If you are unable to re-enable this setting because it is grayed out, then the setting is being managed by group policy. In this situation, please contact your administrator to have this group policy removed.