SYMPTOMS

When an Apple iPhone email client is being used other clients have errors when logging into same mailbox.

CAUSE

When the iPhone connects to a mailbox using POP it will download the smaller messages to the client and will keep the connection alive while you continually check the other often larger messages.  At this time if a message is larger than its internal set limit and has not yet been downloaded it will be done so after you select the message in the Apple iPhone email client.

Because the client has not sent the QUIT command and the connection is not ended it then means by default any new client that connects will be rejected until this initial connection has ended.  With the Apple iPhone even if you stop the application it will still keep the connection open until it's internal time limit is reached.

RESOLUTION

There are a few things that can be changed to help in this situation;

1.  In MailEnable Professional and Enterprise version 2 and onwards there is a feature under the POP properties that allows concurrent access to a mailbox.  This feature means that while one client is connecting it does not create the usual block file to prevent concurrent access.  Not doing this allows multiple clients to download the messages from the inbox at the same time.

2.  You can decrease the timeout value on the POP service, this will force the disconnection of the client earlier if it is not performing any actions.  The default time limit for this feature is 1000 seconds or 16 minutes you can reduce this timeout to a lower value.  (A good place to start is 5 minutes or 300 seconds)

3.  Change your iPhone clients to use the IMAP service for connection rather than POP as the IMAP service is designed for multiple client access where POP is not.

Information on templock file in POP mailbox - http://www.mailenable.com/kb/content/article.asp?ID=ME020018

REFERENCES

MailEnable Manual for any configuration settings: http://www.mailenable.com/references.asp