Microsoft Office Home and Business 2019 - Outlook PST max size

DaveW99 

Have you tried setting the MaxFileSize and WarnFileSize registry keys (to 4090445042 and 4294967295 respectively) as well as the MaxLargeFileSize and WarnLargeFileSize registry keys (to these same two values)?

See Microsoft's own support article at https://support.microsoft.com/en-us/topic/how-to-configure-the-size-limit-for-both-pst-and-ost-files-in-outlook-2f13f558-d40e-9c2a-e3b6-02806fa535f4

The above article also mentions UNICODE vs. ANSI formatted PST/OST files, but doesn't elaborate how (if it's even possible) to convert an existing PST or OST file between these formats, nor what the pros/cons are of each format (or how each format type gets created/used in the first place).

Notwithstanding this, it looks like Outlook 2019 lets you create "Outlook Data File" PST files or "Outlook 97-2002 Data file" PST files - so this may be the answer for you (i.e. you might need to create a new PST file that is NOT formatted in "Outlook 97-2002" format, and then manually drag or copy/move the emails [etc.] in your existing PST file into this new PST file as a one-off task). However, if you do try this, I strongly recommend that you make a backup copy of your existing PST file first (making sure you've closed it in Outlook beforehand, then closed Outlook entirely, and then let Outlook close in your system tray too, of course). Alternatively (and definitely a better way to do this), you can just copy the email (etc.) data into the new PST file by holding down the CTRL key during each drag/copy operation (sorry if you already know this - but it's worth being careful/sure!!).

In particular, the above Microsoft article states the following - which certainly seems to fit the symptom you've reported:

"If the value of the MaxFileSize registry entry ever exceeds the ANSI 2 gigabyte (GB) limit [when using ANSI-formatted PST/OST files] on either the .pst or the .ost files, the value will be ignored to limit the size to 2 GB to prevent corruption."

(I've added the bit in square brackets here, as Microsoft is unhelpfully vague!)

Interestingly, my own PC is running Outlook 2019 and doesn't even have the 4 registry keys mentioned above present AT ALL (nor even the 'path' to HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\Outlook\PST (it just stops one level up at HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\Outlook) - yet Outlook has no problem working with several large PST files that I have, the largest of which is 8 GB in size).