VPOP3 Webmail slow when using Sophos Antivirus

Several users have recently reported that the VPOP3 Webmail is very slow, and they are using Sophos Antivirus on the VPOP3 computer (with appropriate exclusions etc).

We have found that disabling VPOP3's HTTP compression speeds up the access to a large degree. Disabling the compression has the side-effect of making initial download of the Webmail pages much larger (approximately 2.5MB instead of 700kB), but the increased speed more than compensates for that in most cases.

To disable VPOP3's HTTP compression, you should simply rename the 'gzip.exe' file in the VPOP3 installation directory to 'gzip.orig' and delete the contents of the VPOP3\_webmailcache folder. You usually do not need to restart VPOP3.

Note that we are only aware of this making a difference when Sophos Antivirus is installed on the VPOP3 computer. We are unsure why this makes such a huge difference, because VPOP3 has been doing this the same way since about 2011, and it does not seem to affect other users who are not using Sophos Antivirus.