• Messages sent to public folders by PYTHEAS MailGate are stored as a post (IPM.Post), not as a message (IPM.Note) as expected
• Messages sent to a Microsoft Exchange 2007/2010 distribution list are not distributed
• You get a 554 Maximum hop count exceeded - Possible mail loop detected error for incoming messages
• Incoming messages from certain POP3 servers are not correctly decoded by Microsoft Exchange 20xx
• The body of an e-mail message is garbled - incorrect character set used
• The PYTHEAS MailGate Communication Task does not work as expected when running as a service, but works as expected when launched from the Start menu
• The PYTHEAS MailGate Communication Task stops working unexpectedly
• PYTHEAS MailGate does not correctly recognize message priority with Microsoft Exchange 2007
• The PYTHEAS MailGate service does not start at system start-up
• Configuration Program: Deleting messages with the POP3 Account View/Delete messages function does not work
• Outgoing mail handling in v. 2.70: message erroneously reported as "sent"
• Timeout error with empty POP3 mailbox

You can reproduce this problem with the Send test message function on the Recipient property page of the Recipient pointing to the distribution list. The SMTP dialog completes normally.

Please note that this is a Microsoft Exchange 20xx feature, not a PYTHEAS MailGate problem.

We recommend to first check (and count) the Received message header lines of one of such messages. As these are not transmitted successfully to the Exchange server, they remain in the POP3 mailbox, and you can read the message headers after opening the Properties pages of the POP3 account, Delete/Cleanup page, View Delete Messages form, View message headers button. If you do not find any evidence of a loop, proceed as indicated below.

The maximum number of Received headers corresponds to the MaxHopCount parameter of the Exchange Receive Connector listening on port 25 (by default, its name is Default <YourServerName>). To check the current value, issue this Exchange Management Shell command:
[PS] C:\>get-receiveconnector -identity "Default YourServerName" | Format-List
Look for the MaxHopCount value.
To change the value, use the following command:
[PS] C:\>set-receiveconnector -identity "Default YourServerName" -MaxHopCount:40

Historical note: this problem has been observed first with British Telecom BTConnect POP3 accounts, hence the choice of the keyword.

This can happen if the server is very busy at system start-up. Please have a look at http://support.microsoft.com/kb/922918, or it may help to make the Pytheas.MailGate service dependent on some other service which starts up late; you may want to have a look at the application event log to get an idea which one to choose for this purpose. If PYTHEAS MailGate is installed with a Microsoft Exchange 2003/2000 server, its POP3 service (POP3Svc) may be a good candidate. We pick this one as an example here.

To configure the dependency, proceed as follows:
- Open Regedt32.exe (not Regedit.exe);
- Go to HKEY_LOCAL_MACHINE/System/Currentcontrolset/Services/Pytheas.MailGate
- Open the DependOnService value. By default, it has 3 lines: Eventlog, RpcSc, TcpIp.
- Add the line: POP3Svc to the end of the list. This will make the Pytheas.Mailgate service dependent on this service.

The POP3 server does not conform to RFC 1939. Use the Try connection button of the Configuration Program, POP3 account property page, to see the POP3 dialog when the mailbox is empty. Check if you get a dialog like:

+OK IMS POP3 Server 0.87 Ready
USER username
+OK username is welcome here
PASS xxxxxxxxxxx
+OK username's mailbox has 0 message(s) (0 octets)
LIST
+OK 0 message (0 octets)
0 messages (0 octets)

The problem is that the "0 messages (0 octets)" line should not be there, and that the response to the "LIST" command is not terminated by a single point on a line.
Here is what RFC 1939 (POP3, May 1996) says on the subject (we did the bold typesetting):

(...)
Responses to certain commands are multi-line. In these cases, which are clearly indicated below, after sending the first line of the response and a CRLF, any additional lines are sent, each terminated by a CRLF pair. When all lines of the response have been sent, a final line is sent, consisting of a termination octet (decimal code 046, ".") and a CRLF pair.
(...)
LIST [msg]
Arguments: a message-id (optionally) If a message-id is given, it may NOT refer to a message marked as deleted.
Restrictions: may only be given in the TRANSACTION state.

Discussion:
If an argument was given and the POP3 server issues a positive response with a line containing information for that message. This line is called a "scan listing" for that message.
If no argument was given and the POP3 server issues a positive response, then the response given is multi-line. After the initial +OK, for each message in the maildrop, the POP3 server responds with a line containing information for that message. This line is called a "scan listing" for that message. If there are no messages in the maildrop, then the POP3 server responds with no scan listings--it issues a positive response followed by a line containing a termination octet and a CRLF pair.