Why personal folder files (.pst files) are unsupported over a local area network (LAN) or wide area network (WAN) link?

Top 3 reasons why PST’s are not supported on over a network:

1. All operations take longer.

2. Write operations can take approximately four times longer than read operations.

3. Outlook has slower performance than the Exchange Client.

The .pst files are not meant to be a long-term, continuous-use method of storing messages in an enterprise environment. Two alternatives are suggested:

1. Using .ost files 

2.Microsoft Windows Terminal Services.

The Microsoft Exchange Server 4.0 team created .pst files with the intent of letting a person maintain a copy of their messages on their local computer. The .pst files also serve the purpose of a message store for users who do not have access to a Microsoft Exchange Server computer (for example, Microsoft Outlook Internet Mail Only (IMO) mode users). Although it is possible to specify a network directory or a Universal Naming Convention (UNC) path as a storage location for a .pst file, network usage is not meant to be a long-term, continuous-use method of storing messages in an enterprise environment.

A .pst file is a file-access-driven method of message storage, the computer uses special file access commands that the operating system provides to read and write data to the file. This is not efficient on WAN or LAN links, because the operating system has to send those access commands over the network since the file is not on the local computer. This creates a great deal of overhead and increases the time it takes to read and write to the file. Additionally, the use a .pst file over a network connection may result in a corrupted .pst file if the connection degrades or fails.

Reference link: Microsoft Help and Support