Error 10055 means that Windows has run out of TCP/IP socket buffers because too many connections are open at once.
Things to check if this happens are:
- Is there any other TCP/IP software running on the same PC as VPOP3 - eg a proxy server
- If you are using 'MX Sending' (on the Out Mail tab in VPOP3), then we recommend that you use
the latest version of VPOP3 (1.4.0c or later)
- If VPOP3 is running on Windows 95, make sure you have the kernel updates which fixed a resource
problem which could cause this error
- If you have a lot of client computers connecting to VPOP3 either make them connect less frequently,
or make sure you are running VPOP3 on Windows NT or 2000 as that has less of a limit on the number of
We now also believe that the W32/QAZ trojan horse program may be responsible for causing 10055 errors.
We have seen the W32/QAZ trojan horse on several computers which were exhibiting this problem.
Also 10055 errors which weren't related to the above problems have been infrequently reported
and only since the last half of 2000 - the W32/QAZ trojan horse was first noticed in August 2000.
The W32/QAZ trojan horse replaces NOTEPAD.EXE with its own version, and will try to send emails
to a remote user. If this email attempt fails it appears that the socket buffers are not cleaned up
correctly afterwards, causing the 10055 errors later.
Most current email scanners should be able to find the W32/QAZ trojan horse. The trojan can also
be detected by using REGEDIT to look in the registry key:
for a string value of:
startIE "notepad qazwsx.hsq"
For more information on the W32/QAZ trojan you can look at virus scanner developers' websites, eg