Losing AOL mail messages in Outlook 2013 – Microsoft Community

I will help you to configure the AOL email account correctly, so all the emails are displayed. Follow these steps below and check if all the emails appear in inbox for AOL account: Click File, go to Account Settings, in the Email tab click the AOL account to open its properties, set the Mail to Keep Offline to ALL. Hope the suggestion is helpful.

https://answers.microsoft.com/en-us/outlook_com/forum/all/losing-aol-mail-messages-in-outlook-2013/0fad4c77-5497-4539-9116-bcb04acfdd75