Complex sentence: Email users may find the use of both a webmail client and a desktop client using the POP3 protocol a bit incompatible: email messages that are downloaded by the desktop client and are removed from the server will no longer be available on the webmail client.
Split into simpler sentences: Email users may find the use of both a webmail client and a desktop client using the POP3 protocol presents some difficulties. For example, email messages that are downloaded by the desktop client and are removed from the server will no longer be available on the webmail client.