Page 82 - Mercury Manual.book

77 The MercuryP POP3 Server Module
General configuration

The MercuryP POP3 Server Module

MercuryP is the protocol module responsible for providing users with access to their new
mail on the server via the POP3 protocol. It complies with Internet Standards Document
RFC1939, with some extensions.

General configuration

Listen on TCP/IP port Enter here the TCP/IP port on which MercuryP should listen for in-
coming connections. The usual and default value for this field is 110, but you may want to
change this on certain occasions.

Timeout (timeout) the length of time in seconds that MercuryP should wait for data on a con-
nection before assuming that the connection is no longer valid and aborting it.

IP Interface to use If your computer supports multiple IP interfaces, you can use this field
to tell MercuryP which interface it should select when listening for connections: enter the in-
terface as a dotted IP address in the general form www.xxx.yyy.zzz. As an example, your
system may have one IP address assigned to a dialup PPP connection, and another, different
IP address assigned to a local Ethernet network - you would enter here the interface you need
MercuryP to use. If you leave this field blank, MercuryP will listen on all available interfaces.
Unless you are very sure of what you are doing, or have been instructed by an ISP or network
administrator, you should leave this field blank. If you change the IP interface in this field,
you must restart Mercury before the new interface number will be used.

Use 'Daylight Savings-proof' message IDs Without getting too technical, part of the POP3
protocol involves assigning what are known as unique IDs (UIDs) to messages. A message's
UID should never change during its time in the POP3 mailbox and it is intended as a means
by which POP3 client programs can remember whether or not they have seen a particular
message during a previous connection. In the past, Mercury calculated a message's UID
based partly on the file creation time maintained by the Windows operating system, but it
turns out that there is a serious and long-standing bug in Windows that makes this unreliable:
put simply, Windows applies the current Daylight Savings Time (DST) adjustment to all file
timestamps, even files that were created when the DST adjustment did not apply! So, after a
DST change, many files on your hard drive or server will suddenly appear have different
times. This bug impacts on Mercury by throwing out its calculated UIDs: as a result, after a
DST change, your POP3 clients will see new UIDs for the messages in the mailbox and will
typically download them all again. Checking this control tells Mercury to use a different
method of calculating the UIDs for messages - one not affected by the Windows bug, but you
should be aware that changing to it will result in all your POP3 clients re-retrieving all their
mail one last time, as a reaction to the new UIDs that are generated. After that one final re-
dundant download, though, there will be no future occurrences. We strongly recommend that
you check this control as soon as circumstances permit, or if it is already checked, that you
never uncheck it.

Refuse access when no password is defined When this control is checked, MercuryP will
refuse all attempts to login to an account where no password is provided. This effectively dis-
ables access to accounts without a password: because this is almost always an important se-
curity issue, this control is enabled by default.